Optical storage medium, optical read/write apparatus, and optical read/write method

ABSTRACT

An optical read/write apparatus causes a read/write light beam from illuminating means to strike only one side of an optical storage medium including stacked data storage layers each of which is readable/writeable separately from the other layers. In this case, the optical read/write apparatus operates so that data is read/written from/into a second data storage layer after fully recording a recordable area of a first data storage layer. Thus, light can be shone with uniform intensity across the substantially entire recordable area of the second data storage layer without using a complex read/write system even under such conditions that the transmittance to light of the first data storage layer in the recordable area may vary depending on whether any data is recorded in the recordable area.

FIELD OF THE INVENTION

[0001] The present invention relates to optical storage media having aplurality of writeable and/or readable data storage layers, opticalread/write apparatus using such media, and optical read/write methodusing such media.

BACKGROUND OF THE INVENTION

[0002] Recent years have seen on-going development of optical read/writeapparatus capable of writing a large amount of data, like video data indigital format, and randomly accessing such data. Also, various attemptsare being made to increase the storage density of optical disks used asstorage media in such optical read/write apparatus.

[0003] In optical read/write apparatus, attempts are being made toincrease storage density by means of, for example, an increasednumerical aperture of an objective lens and the use of short wavelengthillumination for a smaller light beam spot. The efforts have beensuccessful and the storage capacity optical disks are getting largeryear after year. Technology has already established as to a DVD-ROM(Digital Versatile Discs for Read Only Memory) as an optical disk whichnow has doubled its capacity owning to double layer structure.

[0004] A document entitled “A 16.8GB Double-Decker Phase Change Disc”distributed in Joint International Symposium on Optical Memory andOptical Data Storage 1999 discloses an optical disk with an addeddensity thanks to the double data storage layers which are writeable andreadable.

[0005] In the optical disk disclosed in the document, each data storagelayer is made of phase change material. Such optical disks areclassified into two types: Low-to-high media which has a higherreflectance in recording mark areas than in interval areas interposedbetween recording mark areas and high-to-low media which conversely hasa higher reflectance in interval areas than in recording mark areas.Both types of media enable the readout of data by means of quantities ofreflected and transmitted light which vary depending on whether thephase change material is in polycrystal or amorphous phase. Similaroptical disks using phase change material are disclosed in, for example,Japanese Laid-open Patent Application 2001-52342 (Tokukai 2001-52342,published on Feb. 23, 2001).

[0006] However, for example, on the high-to-low medium having a higherreflectance in interval areas than in recording mark areas, mark rowswhich include low reflectance amorphous areas are formed along guidinggrooves in recorded areas. In the optical disk, data is written or readon a first data storage layer close to the light-striking side and on asecond data storage layer far from the light-striking side using lightincident to the same side of the disk, the light beam first travelsthrough the first data storage layer before writing or reading data onthe second data storage layer. Accordingly, upon writing or reading onthe second data storage layer, the intensity of light beam reaching thesecond data storage layer after passing through the first data storagelayer must differ depending on whether or not the first data storagelayer already holds any records, so as to produce different writing orreading power sensitivities with respect to the second data storagelayer.

[0007] Therefore, to write or read data on the second data storagelayer, the first data storage layer must be checked first to determinewhether there are any records on it, so that the write or read lightbeam intensity can be specified. This adds complexity to the write/readsystem. A problems arises here that optical writing/reading system usingsuch an optical disk is hardly practicable.

[0008] As mentioned above, Japanese Laid-open Patent Application2001-52342 discloses an optical disk having a double data storage layerstructure in which address information is provided in the form ofwobbling groove so as to achieve stable writing and readout.

[0009] Referring to FIG. 64, an optical disk 501 provided withconventional double data storage layers has a center hole 502 at thecenter. Data is written/read in a recordable area 503 in which a spiralguiding groove is provided for data write and readout.

[0010] The optical disk 501 has an address area 504 occupying a certainangular part. Address information is stored in the address area 504 asaddress pit rows extending radially. Throughout this text, thisconfiguration, in which address information is stored collectively inone place, i.e., the address area 504 in the case of the optical disk501, will be referred to as a lumped address scheme.

[0011]FIG. 65 shows the optical disk 501 in vertical cross section. Theoptical disk substrate 506 has thereon a guiding-groove-formed layer 507on whose surface a spiral guiding groove is formed from depressions andprojections, a second storage layer 508, a guiding-groove-formedintermediate layer 509, a first storage layer 510, surface-coating layer511 which are deposited in the order. To write/read data on the firststorage layer 510 and the second storage layer 508 in the optical disk501, a focused light beam 512 is shone onto the first and second storagelayers 510, 508 via only one side of the disk, that is, the side of thesurface-coating layer 511.

[0012]FIG. 66 shows an enlarged view of a guiding groove 513 and a partof address pit rows 515 in the address area 504. On the optical disk501, recording marks 1114 are formed along the spiral guiding groove513, and the address pit rows 515 are formed extending from the guidinggroove 513 in the address area 504.

[0013] To read/write data on the first storage layer 510 in the opticaldisk 501, as shown in FIG. 67, the light beam 512 to focused toilluminate the first storage layer 510 by means of tracking along theguiding groove 513 on the first storage layer 510 while controlling theintensity of the light beam. To read/write data on the second storagelayer 508, the light beam 512 is focused to illuminate the secondstorage layer 508 by means of tracking along the guiding groove 513 onthe second storage layer 508 while controlling the intensity of thelight beam.

[0014] Under these conditions, let us suppose that the optical disk 501is a phase change storage medium of a high-to-low type in which, forexample, interval areas have high reflectance, i.e., lowertransmittance, than the recording marks 1114 on the first storage layer510 and the second storage layer 508.

[0015] In the event, to read/write data on the second storage layer 508,a light beam 512 d passes through the area where there is the guidinggroove 513 on the first storage layer 510 and is focused onto the secondstorage layer 508, only after having passed through the area where thereexist the recording marks 1114 which have relatively bettertransmittance. In contrast, a light beam 512 d passes through theaddress area 504 of the first storage layer 510 and is focused onto thesecond storage layer 508, only after having passed through the areawhere there are no recording marks 1114 which have higher transmittance,that is, a low transmittance area. Therefore, the intensity of the lightbeam 512 e having passed through the area where there is the guidinggroove 513 on the first storage layer 510 becomes greater than that ofthe light beam 512 d having passed through the address area of the firststorage layer 510.

[0016] Therefore, referring back to FIG. 66, as to the optical disk 501having address area where address pit rows 515 are lumped together, theintensity of a light beam focused onto the second storage layer 508varies between the address area 504 and the other area where the guidinggroove 513 is provided. This makes it impossible perform stablewrite/readout.

[0017] To solve these problems, in the aforementioned prior art patentpublication, no address area 504 with address pit rows 515 in FIG. 66 isprovided. Instead, it suggests that the variations in intensity of thelight beam focused on the second storage layer 508 be restrained byproviding a wobbling guiding groove to record address information in theform of wobbles. Throughout this text, the configuration, in whichaddress information is not stored collectively in one place, butdistributed will be referred to as a distributed address scheme.

[0018] However, in the configuration disclosed in the prior art patentpublication, address information is stored on the guiding groove in theform of its wobbles. Therefore, the guiding groove needs be scanned overa relatively long period of time to retrieve a single set of addressinformation.

[0019] Specifically, each address pit in the address pit rows 515 inFIG. 66 has a diameter which is more or less equal to the width of theguiding groove 513: typically, 0.3 microns to 0.5 microns, and each setof address information is recorded over about 1 mm or less of theguiding groove 513 in the address area 504.

[0020] In contrast, in the case of wobbling guiding grooves, to ensurethat the quantity of reflected light does not vary in tracking, eachwobble must be several tens of microns long, that is, each address areastoring a set of address information must be about 100 mm long in awobbling guiding groove.

[0021] In a lumped address scheme using address pit rows 515, addressinformation is completely reproduced when about 1 mm or less of theaddress area is scanned. Meanwhile, in a distributed address schemeusing a wobbling guiding groove, address information is completelyreproduced only when about 100 mm of the guiding groove is scanned,which is relatively long. Distributed address scheme is therefore not toachieve high speed randomly access in optically reading/writing data onoptical disks. Lumped address scheme should hence be employed toreproduce address information instantly.

[0022] Now referring to FIG. 68, another conventional optical disk 601has a center hole 602, a recordable area 603, innermost part 604, anoutermost part 605, and prepit areas 606.

[0023] The optical disk 601 is provided with a guiding groove (notshown) which is, for example, spiral. Tracking is done along the guidinggroove to read/write data in the recordable areas 603 by shining a lightbeam 621 onto first and second storage layers (double layers) 611, 612as shown in FIG. 69. In the prepit areas 606, or the inner prepit area606 a and outer prepit area 606 b, of the first and second storage layer611, 612, are there formed pit rows (not shown) which form, for example,a spiral. Tracking is done along the pit rows, and a light beam 621 isshone to reproduce prerecorded information from the pit rows.

[0024]FIG. 70 shows an enlarged view around the border between therecordable area 603 and a prepit area 606. FIG. 71 shows its crosssection in which only the first storage layer 611 and the second storagelayer 612 are depicted. The following description assumes that the firstand second storage layers 611, 612 are formed in a phase change storagemedium of a low-to-high type whose transmittance is higher in producedrecording marks than in non-recorded areas.

[0025] As shown in FIG. 70 and FIG. 71, if the first storage layer 611,located on the light-striking side, has a prepit area 606, light beams621 a, 621 b are focused and shone onto the second storage layer 612after recording marks M are formed along the guiding groove G in therecordable area 603 of the first storage layer 611. In this case,intensity differs between the light beam 621 a, which is transmittedthrough the recordable area 603 and then focused, and the light beam 621b, which is transmitted through the prepit area 606 and then focused.

[0026] In the recordable area 603 do there exist multiple recordingmarks M with high transmittance, and the light beam 621 a transmittedthrough the recordable area 603 of the first storage layer 611 has arelatively high intensity. In the prepit area 606 do there exist norecording marks M, and the light beam 621 b transmitted through theprepit area 606 of the first storage layer 611 has a relatively lowintensity. As could be understood from this, the provision of a prepitarea 606 in the first storage layer 611 causes undesirable variations inreading/writing power in reading/writing and makes it impossible toread/write data on the second storage layer 612 in a stable manner.

SUMMARY OF THE INVENTION

[0027] The present invention has an objective to offer an opticalstorage medium, an optical read/write apparatus, and an opticalread/write method, with which light can be shone with uniform intensityacross the substantially entire recordable area of the second datastorage layer without using a complex read/write system even under suchconditions that the transmittance to light of the first data storagelayer in the recordable area may vary depending on whether any data isrecorded in the recordable area.

[0028] In order to achieve the foregoing object, an optical storagemedium of the present invention includes stacked data storage layerseach of which is readable/writeable separately from the other layers bymeans of only a light beam striking one side of the optical storagemedium, and is characterized in that a recordable area of a first datastorage layer has adjacent to an end thereof an extended area coveringmore than an area directly above a recordable area of a second datastorage layer in a direction in which the first and second data storagelayers are stacked, the first data storage layer being one of the datastorage layers which is located closest to a light-striking surface ofthe medium, the second data storage layer being another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface.

[0029] According to the arrangement, the recordable area of the firstdata storage layer has adjacent to an end thereof an extended areacovering more than an area directly above a recordable area of a seconddata storage layer in a direction in which the first and second datastorage layers are stacked. Therefore, if data is read/written from/inthe recordable area of the second data storage layer after fullyrecording the recordable area of the first data storage layer,substantially all the read/write light striking the second data storagelayer after passing through the first data storage layer passes throughthe recorded recordable area of the first data storage layer uponreading/writing on the second data storage layer.

[0030] Therefore, light can be projected at uniform intensity onsubstantially all recordable areas of the second data storage layer evenwhen the optical transmittance of the recordable area of the first datastorage layer varies depending whether the recordable area is fullyrecorded or not. Therefore, desirable read/write characteristics can beimparted without using a complex read/write system.

[0031] An optical read/write apparatus of the present invention causes aread/write light beam from illuminating means to strike only one side ofan optical storage medium, and is characterized in that the apparatusincludes controlling means for controlling the illuminating means sothat the extended area of the optical storage medium is fully recordedbefore a recordable area of the first data storage layer of the opticalstorage medium is recorded except for the extended area.

[0032] An optical read/write method of the present invention includesthe step of fully recording the extended area before recording arecordable area of the first data storage layer of the optical storagemedium except for the extended area.

[0033] According to the arrangement, since the optical storage mediumhas an extended area in the recordable area of the first data storagelayer, light can be projected at uniform intensity on substantially allrecordable areas of the second data storage layer. Therefore, desirableread/write characteristics can be imparted without using a complexread/write system.

[0034] The part of the recordable area of the first data storage layerother than the extended area is as large as the recordable area of thesecond data storage layer. The illuminating means is controllable interms of its position relative to the optical storage medium in the samemanner in reading/writing in the part of the recordable area of thefirst data storage layer other than the extended area and the recordablearea of the second data storage layer.

[0035] Another object of the present invention is to provide an opticalstorage medium, an optical read/write apparatus, and an opticalread/write method, with which a desirable reading/writing property canbe realized in an arrangement, using a lumped address scheme, whichincludes data storage layers.

[0036] In order to achieve the foregoing object, an optical storagemedium of the present invention includes stacked data storage layerseach of which is readable/writeable separately from the other layers bymeans of only a light beam striking one side of the optical storagemedium, and each of the data storage layers has at least one addressarea where there are collectively formed address information portionsrepresenting address information, and the optical storage mediumexhibits an optical transmittance which varies when data is written bymeans of the light beam, wherein the address area of a first datastorage layer includes a recorded area exhibiting a varied transmittanceand a non-recorded area exhibiting an original transmittance, and thefirst data storage layer is one of the data storage layers which islocated closest to a light-striking surface of the medium, and a seconddata storage layer is another of the data storage layers which islocated next to the first data storage layer, opposite thelight-striking surface.

[0037] An optical read/write apparatus of the present invention causes aread/write light beam from illuminating means to strike only one side ofan optical storage medium including stacked data storage layers each ofwhich is readable/writeable separately from the other layers by means ofonly a light beam striking one side of the optical storage medium, andeach of the data storage layers has at least one address area wherethere are collectively formed address information portions representingaddress information, and the optical storage medium exhibits an opticaltransmittance which varies when data is written by means of the lightbeam, and the optical read/write apparatus includes controlling meansfor controlling the illuminating means so that the address area of afirst data storage layer includes a recorded area exhibiting a variedtransmittance and a non-recorded area exhibiting an originaltransmittance, and the first data storage layer is one of the datastorage layers which is located closest to a light-striking surface ofthe medium, and a second data storage layer is another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface.

[0038] An optical read/write method of the present invention includesthe step of causing a read/write light beam to strike only one side ofan optical storage medium including stacked data storage layers each ofwhich is readable/writeable separately from the other layers by means ofonly a light beam striking one side of the optical storage medium, andeach of the data storage layers has at least one address area wherethere are collectively formed address information portions representingaddress information, and the optical storage medium exhibits an opticaltransmittance which varies when data is written by means of the lightbeam, wherein the address area in a first data storage layer includes arecorded area exhibiting a varied transmittance and a non-recorded areaexhibiting an original transmittance, and the first data storage layeris one of the data storage layers which is located closest to alight-striking surface of the medium, and a second data storage layer isanother of the data storage layers which is located next to the firstdata storage layer, opposite the light-striking surface.

[0039] According to the arrangement, upon writing or reading on thesecond data storage layer, the intensity of light beam reaching thesecond data storage layer after passing through the address area of thefirst data storage layer on the light-striking side can be made to bealmost the same as the intensity of a light beam reaching the seconddata storage layer after passing through the non-address area in therecordable area of the first data storage layer. As a result, it ispossible to read/write data from/in the second data storage layersteadily and desirably.

[0040] That is, as to the optical storage medium, the non-address areain the recordable area of the first data storage layer has a recordedarea, for example, a recording mark is formed, so that the opticaltransmittance varies at the portion. In a case where the address areadoes not have the recorded area exhibiting a varied transmittance, uponreading or writing on the second data storage layer, there is a greatdifference between the intensity of the light beam reaching the seconddata storage layer after passing the non-address area and the intensityof the light beam reaching the second data storage layer after passingthe address area.

[0041] On the other hand, the present invention is arranged so that theaddress area in the first data storage layer of the optical storagemedium includes a recorded area exhibiting a varied transmittance and anon-recorded area exhibiting an original transmittance. Thus, also inthe address area, an optical transmittance is varied due to the recordedarea as in the non-address area. Therefore, as described above, theintensity of the light beam reaching the second data storage layer afterpassing through the address area of the first data storage layer on thelight-striking side can be made to be almost the same as the intensityof light beam reaching the second data storage layer after passingthrough the non-address area in the recordable area of the first datastorage layer. As a result, it is possible to read/write data from/inthe second data storage layer steadily and desirably.

[0042] According to the optical read/write apparatus or the opticalread/write method, in a case where the recorded area is formed on theaddress area in the first data storage layer of the optical storagemedium, it is possible to manufacture the optical storage medium at alower cost since the manufacturing process of the optical storage mediumis simplified.

[0043] Further, still another object of the present invention is toprovide an optical storage medium, an optical read/write apparatus, andan optical read/write method, with which data can be read/writtensteadily without being influenced by a prepit area. This is realized inan optical disc having two or more storage layers.

[0044] In order to achieve the foregoing object, an optical storagemedium of the present invention includes: one light-striking-sidestorage layer provided as a data storage layer on a light-striking side;and one or more opposite-side storage layers provided as data storagelayers opposite the light-striking side from the light-striking-sidestorage layer, wherein, in order to solve the foregoing problems, one ofthe opposite-side storage layers which is, as a last data storage layer,most distanced from the light-striking-side storage layer has a prepitarea which includes preformed pits representative of data.

[0045] According to the arrangement, since the last data storage layer,most distanced from the light-striking-side storage layer, has a prepitarea, intensity of the striking light is not varied by the prepit area.Thus, it is possible to read/write data from/in the last data storagelayer steadily without being influenced by the prepit area.

[0046] An optical read/write apparatus of the present invention causes aread/write light beam from an illuminating section to strike only oneside of the optical storage medium, wherein the optical read/writeapparatus includes: the optical read/write apparatus includes: anenvelope detecting section for detecting an envelope of a reproductionsignal obtained from the prepit area; a mean level producing section forproducing a mean level of the detected envelope; and a digitalconverting section for converting the reproduction signal to a digitalsignal using the mean level as a reference.

[0047] An optical read/write method of the present invention causes aread/write light beam from an illuminating section to strike only oneside of the optical storage medium, wherein the method further includesthe steps of: producing a mean level of an envelope of a reproductionsignal obtained from the prepit area; and converting the reproductionsignal to a digital signal using the mean level as a reference.

[0048] According to the foregoing apparatus and method, an envelope of areproduction signal obtained when the prepit area is reproduced isdetected by the envelope detecting section. Then, the mean levelproducing section produces a mean level of the detected envelope.Thereafter, the digital converting section converts the reproductionsignal to a digital signal using the mean level as a reference. Thus,the mean level is always detected, and the detected mean level is usedas a reference in the digital conversion, so that it is possible toperform the digital conversion without being influenced by variance inamplitude of the reproduction signal. For example, in a case where thereexist a fully recorded portion exhibiting high transmittance afterrecording and an unrecorded portion which holds no record, when a lightbeam that is projected so as to cover the fully recorded portion and theunrecorded portion is focused on the second storage layer, it ispossible to steadily obtain a digital signal from the reproductionsignal even though the reproduction signal strength of prepit datavaries in connection with rotation of the optical storage medium. Thus,it is possible to-steadily reproduce the prepit data on the secondstorage layer of the optical storage medium.

[0049] For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0050]FIG. 1 is a vertical cross-sectional view illustrating how anoptical-disk-read/write apparatus of an embodiment of the presentinvention reads/writes data on the second storage layer of an opticaldisk.

[0051]FIG. 2 is a plan view of the optical disk shown in FIG. 1.

[0052]FIG. 3 is a vertical cross-sectional view showing the structure ofthe optical disk shown in FIG. 1.

[0053]FIG. 4 is an enlarged vertical cross-sectional view showing amajor part of the optical disk shown in FIG. 3 in more detail.

[0054]FIG. 5 depicts the structure of an optical-disk-read/writeapparatus of an embodiment of the present invention.

[0055]FIG. 6 depicts the optical disk shown in FIG. 2 on which arecorded area occupies a part of the recordable area of the firststorage layer.

[0056]FIG. 7 is a vertical cross-sectional view illustrating how data isread/written on the second storage layer of the optical disk shown inFIG. 6.

[0057]FIG. 8 is a block diagram showing a configuration by which data isread/written on the second storage layer after the first storage layerof the optical disk in FIG. 1 is fully recorded by means of the signalprocessing and controlling unit shown in FIG. 5.

[0058]FIG. 9 depicts the structure of the first and second storagelayers of an optical disk of an embodiment of the present invention andhow data is read/written on the second storage layer.

[0059]FIG. 10 is a vertical cross-sectional view showing an optical diskwhich has the first and second storage layers shown in FIG. 9.

[0060]FIG. 11 depicts the structure of the first and second storagelayers of an optical disk which is a comparative example of the opticaldisk shown in FIG. 9 and how data is read/written on the second storagelayer.

[0061]FIG. 12 depicts the structure of the first and second storagelayers of an optical disk of another embodiment of the present inventionand how data is read/written on the second storage layer.

[0062]FIG. 13 is a vertical cross-sectional view showing an optical diskequipped with the first and second storage layers shown in FIG. 12.

[0063]FIG. 14 is a block diagram showing the configuration of part ofthe signal processing and controlling unit shown in FIG. 5 by which anextended area of the optical disk shown in FIG. 9 is fully recorded.

[0064]FIG. 15 is a block diagram showing the configuration of part ofthe signal processing and controlling unit shown in FIG. 5 by which datais encrypted before written on the optical disk.

[0065]FIG. 16 is a block diagram showing the configuration of part ofthe signal processing and controlling unit shown in FIG. 5 by whichapparatus ID information is recorded in an extended area of the opticaldisk shown in FIG. 9.

[0066]FIG. 17 is a block diagram showing the configuration of part ofthe signal processing and controlling unit shown in FIG. 5 by whichencryption code information is recorded in an extended area of theoptical disk shown in FIG. 9.

[0067]FIG. 18 is a block diagram showing the configuration of part ofthe signal processing and controlling unit shown in FIG. 5 by whichactions are taken according to whether or not the apparatus IDinformation stored in an extended area of the optical disk shown in FIG.9 matches the apparatus ID information of the optical-disk-read/writeapparatus.

[0068]FIG. 19 is a block diagram showing the configuration of part ofthe signal processing and controlling unit shown in FIG. 5 by whichencrypted information stored on the optical disk is decrypted.

[0069]FIG. 20 is a block diagram showing the configuration of part ofthe signal processing and controlling unit shown in FIG. 5 by which datais test written in an extended area of the optical disk shown in FIG. 9.

[0070]FIG. 21 is an enlarged view showing part of a recordable area andan address area of an optical disk as an optical storage medium of afurther embodiment of the present invention.

[0071]FIG. 22 depicts how data is read/written in the recordable areaand the address area of the second storage layer shown in FIG. 21.

[0072]FIG. 23 is a plan view of the optical disk shown in FIG. 21.

[0073]FIG. 24 is a block diagram showing the configuration of part of asignal processing and controlling unit in an optical-disk-read/writeapparatus of the present embodiment by which a continuous storage areais formed in an address area of the optical disk shown in FIG. 21 basedon a rotation synchronized signal.

[0074]FIG. 25 is a block diagram showing the configuration of part ofthe signal processing and controlling unit by which a continuous storagearea is formed in an address area of the optical disk shown in FIG. 21based on address information.

[0075]FIG. 26 is an enlarged view showing part of a recordable area,address area, and judgement mark area of an optical disk as an opticalstorage medium of still a further embodiment of the present invention.

[0076]FIG. 27 is a block diagram showing the configuration of part ofthe signal processing and controlling unit by which a continuous storagearea is formed based on a signal reproduced from the judgement mark areaof the optical disk shown in FIG. 26.

[0077]FIG. 28 is an enlarged view showing part of a recordable area andan address area of an optical disk as an optical storage medium ofanother embodiment of the present invention.

[0078]FIG. 29 is a block diagram showing the configuration of part ofthe signal processing and controlling unit by which a continuous storagearea is formed on the optical disk shown in FIG. 28 based on a trackingservo signal.

[0079]FIG. 30 is an enlarged view showing part of a recordable area andan address area of an optical disk as an optical storage medium ofanother embodiment of the present invention.

[0080]FIG. 31 is a block diagram showing the configuration of part ofthe signal processing and controlling unit by which a continuous storagearea is formed on the optical disk shown in FIG. 30 based on an addressinformation reproduction signal.

[0081]FIG. 32 is an enlarged vertical cross-sectional view showing thestructure of a part of the first storage layer and the second storagelayer which has a prepit area in an optical disk of another embodimentof the present invention.

[0082]FIG. 33 is a plan view showing common features in the structure ofoptical disks of another embodiment of the present invention.

[0083]FIG. 34 is a vertical cross-sectional view showing the structureof those types of optical disks which light enters on theirsurface-coating layer sides, among the foregoing optical disks.

[0084]FIG. 35 is an enlarged vertical cross-sectional view showing thestructure of a major part in FIG. 34.

[0085]FIG. 36 is a perspective view showing the structure of aguiding-groove-and-pits-formed layer and a part of aguiding-groove-and-pits-formed intermediate layer where a guiding grooveis formed on the optical disk.

[0086]FIG. 37 is a perspective view showing the structure of aguiding-groove-and-pits-formed layer and a part of aguiding-groove-and-pits-formed intermediate layer where pits are formedon the optical disk.

[0087]FIG. 38 is a vertical cross-sectional view showing the structureof those types of optical disks which light enters on their disksubstrate sides, among the foregoing optical disks.

[0088]FIG. 39 is a plan view showing the first storage layer of theoptical disk shown in FIG. 34 is partly recorded.

[0089]FIG. 40 is a vertical cross-sectional view showing light beamsbeing transmitted through a recorded part and a non-recorded part of theoptical disk shown in FIG. 39 before focused on the second storagelayer.

[0090]FIG. 41 is a vertical cross-sectional view showing light beamstransmitted through the first storage layer which is fully recordedbefore being focused on the second storage layer, in the optical diskshown in FIG. 39.

[0091]FIG. 42 is an enlarged vertical cross-sectional view showing apart of the optical disk shown in FIG. 39, where data is recorded on apart of a recordable area of the first storage layer, and light beamsare focused on prepits on the second storage layer.

[0092]FIG. 43 is an enlarged plan view of FIG. 42.

[0093]FIG. 44 is a graph showing, under the conditions illustrated inFIG. 42, the relationship between the angular position of an opticaldisk and the intensity (envelope) of a reproduction signal of prepitinformation when a light beam is projected partly covering both arecorded part and a non-recorded part in a recordable area of the firststorage layer.

[0094]FIG. 45 is a waveform chart showing, under the conditionsillustrated in FIG. 42, the relationship between the angular position (0degrees and 180 degrees) of optical disk and the intensity of areproduction signal of prepit information when a light beam is projectedpartly covering both a recorded part and a non-recorded part in arecordable area of the first storage layer.

[0095]FIG. 46 is a waveform chart showing, under the conditionsillustrated in FIG. 44, the relationship between the angular position ofan optical disk and the intensity of a reproduction signal of prepitinformation, where the envelope has a mean, slice level.

[0096]FIG. 47 is a block diagram showing the configuration of areproduction circuit which produces a digital signal from a reproductionsignal using the slice level shown in FIG. 46.

[0097]FIG. 48 is a graph showing, under the conditions illustrated inFIG. 42, the relationship between the angular position of an opticaldisk and the intensity (envelope) of a reproduction signal of prepitinformation when a light beam is projected partly covering both arecorded part and a non-recorded part in a recordable area of the firststorage layer, where the reproduction signal is rid of low frequencyvariations.

[0098]FIG. 49 is a block diagram showing the configuration of areproduction circuit which produces a digital signal based on theenvelope shown in FIG. 48.

[0099]FIG. 50 is an enlarged vertical cross-sectional view showing thestructure of a part of the optical disk shown in FIG. 42, where thefirst storage layer has a pseudo-recording area.

[0100]FIG. 51 is an enlarge plan view showing the structure of thepseudo-recording area.

[0101]FIG. 52 is a block diagram showing the configuration by which thepseudo-recording area is formed.

[0102]FIG. 53 is an enlarge vertical cross-sectional view showing thestructure of a part of the optical disk of an embodiment of the presentinvention, where the first and second storage layers having a prepitarea.

[0103]FIG. 54 is an enlarged vertical cross-sectional view showing thestructure of a part of the optical disk of FIG. 53, where the secondstorage layer has an extended blank area.

[0104]FIG. 55 is a plan view showing the structure of a part of theoptical disk shown in FIG. 33, where the prepit area is replaced by aprepit area in which is there provided a continuous storage area.

[0105]FIG. 56 is an enlarged vertical cross-sectional view showing thestructure of a part of the first and second storage layer in the opticaldisk shown in FIG. 55.

[0106]FIG. 57 is an enlarged plan view around the border between arecordable area and a prepit area of the first storage layer in theoptical disk shown in FIG. 55.

[0107]FIG. 58 is an enlarged vertical cross-sectional view around theborder shown in FIG. 57, where light beams pass through a recordablearea and a prepit area of the first storage layer before being focusedon the second storage layer.

[0108]FIG. 59 is a block diagram showing a configuration by which thecontinuous storage area is formed.

[0109]FIG. 60 is an enlarged vertical cross-sectional view showing thestructure of a part of the first and second storage layers, as well asthe third storage layer having a prepit area, of an optical disk ofanother embodiment of the present invention.

[0110]FIG. 61 is an enlarged vertical cross-sectional view showing thestructure of a part of the optical disk shown in FIG. 60, where thefirst and second storage layers have a pseudo-recording area.

[0111]FIG. 62 is an enlarged vertical cross-sectional view showing thestructure of a part of the first storage layer which has a prepit areaand the second and the third storage layers which do not, in an opticaldisk of another embodiment of the present invention.

[0112]FIG. 63 is an enlarged vertical cross-sectional view showing thestructure of a part of the optical disk shown in FIG. 62, where theprepit area is replaced by a prepit area in which is there provided acontinuous storage area.

[0113]FIG. 64 is a plan view showing a conventional optical disk.

[0114]FIG. 65 is a vertical cross-sectional view showing the structureof the optical disk shown in FIG. 64.

[0115]FIG. 66 is an enlarged view showing a part of a recordable areaand an address area of the optical disk shown in FIG. 64.

[0116]FIG. 67 depicts the readout and write in a recordable area and anaddress area of the second storage layer shown in FIG. 66.

[0117]FIG. 68 is a plan view showing the structure of anotherconventional optical disk.

[0118]FIG. 69 is an enlarge vertical cross-sectional view showing lightbeams being focused on the first and second storage layer in the opticaldisk shown in FIG. 68.

[0119]FIG. 70 is an enlarge plan view around the border between arecordable area and a prepit area of the first storage layer in theoptical disk shown in FIG. 68.

[0120]FIG. 71 is an enlarge plan view showing light beams being focusedon the second storage layer after transmitted through the first storagelayer in the optical disk shown in FIG. 69.

DESCRIPTION OF THE EMBODIMENTS EMBODIMENT 1

[0121] The following will describe an embodiment of the presentinvention in reference to FIGS. 1-8.

[0122] Referring to FIG. 2, an optical disk (optical storage medium) 1of the present embodiment has a center hole 2 at its center and arecordable area 3 relatively close to the circumference in relation tothe center hole 2. On the recordable area 3, a spiral read/write guidinggroove is formed enabling data readout and write. Broken lines in thefigure indicates an innermost part 4 and an outermost part 5 of therecordable area 3.

[0123] Referring to FIG. 3 showing a vertical cross-sectional view ofthe optical disk 1, the disk 1 has on a disk substrate 6 aguiding-groove-formed layer 7, a second storage layer (second datastorage layer) 8, a guiding-groove-formed intermediate layer 9, a firststorage layer (first data storage layer) 10, and a surface-coating layer11, all the layers being stacked in this order. To read/write data inthe first storage layer 10 or the second storage layer 8 of the opticaldisk 1, a light beam 12 is always projected on the same side of the disk1, i.e., the side where the surface-coating layer 11 is provided, sothat the light beam is concentrated on the targeted, first or secondstorage layer 10, 8.

[0124] The structure of the optical disk 1 is shown in FIG. 4 in moredetail. In the figure, the disk substrate 6 is made of, for example, atransparent polycarbonate substrate which is 1.2 mm thick. Theguiding-groove-formed layer 7 is made of, for example, anultraviolet-ray-setting resin layer which is 20 microns thick. On thesurface of the layer 7 which interfaces the second storage layer 8, aspiral guiding groove 13 is formed from depressions and projections. Theguiding-groove-formed layer 7 is formed, for example, by a patterntransfer technology termed 2P method.

[0125] The second storage layer 8 is made up of, for example, anAlTi-alloy reflective film 14, a ZnS—SiO₂ interference film 15, a SiNprotective film 16, a GeSbTe phase change recording layer 17, a SiNprotective film 18, and a ZnS—SiO₂ interference film 19. These layersare sequentially stacked on the guiding-groove-formed layer 7 bysputtering.

[0126] As with the guiding-groove-formed layer 7, theguiding-groove-formed intermediate layer 9 is made of, for example, anultraviolet-ray-setting resin layer which is 20 microns thick. On thesurface of the intermediate layer 9 which interfaces the first storagelayer 10, the guiding groove 13 is formed. The guiding-groove-formedlayer 9 is again similarly formed, for example, by a pattern transfertechnology termed 2P method.

[0127] As with the second storage layer 8, the first storage layer 10 ismade up of, for example, a ZnS—SiO₂ interference film 20, a SiNprotective film 21, a GeSbTe phase change recording layer 22, a SiNprotective film 23, and a ZnS—SiO₂ interference film 24. These layersare sequentially stacked on the guiding-groove-formed intermediate layer9 by sputtering.

[0128] The surface-coating layer 11 is made of, for example, anultraviolet-ray-setting resin layer which is 80 microns thick. To formthe layer 11, an ultraviolet-ray-setting resin is applied on the firststorage layer 10 by spin coating and then cured by ultraviolet rayillumination.

[0129] The optical disk substrate 6 is, as mentioned in the foregoing, atransparent polycarbonate substrate. However, if the light beam 12 isincident only to the side of the surface-coating layer 11 as is the casewith the optical disk 1 of the present embodiment, the disk substrate 6is not necessarily transparent and may be an opaque metallic substrate.

[0130] The optical disk 1 of the present embodiment has theguiding-groove-formed layer 7 with the guiding groove 13, and theguiding-groove-formed layer 7 is formed by 2P method. Alternatively, forexample, the optical disk 1 may be formed by preparing the disksubstrate 6 by injection molding and directly forming the guiding groove13 on the optical disk substrate 6, in which case theguiding-groove-formed layer 7 is unnecessary.

[0131] The surface-coating layer 11 is formed on the first storage layer10 by spin coating. Alternatively, the layer 11 may be a transparentsheet of uniform thickness pasted onto the first storage layer 10.

[0132] The optical disk 1 has the guiding-groove-formed layer 7, thesecond storage layer 8, the guiding-groove-formed intermediate layer 9,the first storage layer 10, and the surface-coating layer 11sequentially stacked on the optical disk substrate 6. Alternatively, thelayers may be stacked on the optical disk substrate 6 in the order tothe guiding-groove-formed layer 7, the first storage layer 10, theguiding-groove-formed intermediate layer 9, the second storage layer 8,and the surface-coating layer 11, with the light beam 12 being projectedonto the side on which the optical disk substrate 6 is located, in whichcase the films which will eventually constitute the first storage layer10 and the second storage layer 8 must be formed in the reverse orderfrom the case illustrated in FIG. 4.

[0133] An optical-disk-read/write apparatus (optical read/writeapparatus) to read/write data on the optical disk 1 has the structureshown in FIG. 5. In the optical-disk-read/write apparatus 31, theoptical disk 1 is fixed to the spindle 33 of the motor at the center huband rotated.

[0134] The optical-disk-read/write apparatus 31 includes an opticalsystem unit 34 and a signal processing and controlling unit (controllingmeans) 35. The optical system unit 34 includes an illumination source41, such as a semiconductor laser, a collimator lens 42, a beam splitter43, an objective lens 44, a double-axis actuator 45, a collective lens46 and a light-receiving element 47. The objective lens 44 is supportedby the double-axis actuator 45 and moved along a focusing direction anda tracking direction. The light-receiving element 47 includes areproduction signal detecting element, a focus error signal detectingelement, and a tracking error signal detecting element. The outputs ofthe detecting elements are fed to the signal processing and controllingunit 35.

[0135] The optical system unit 34 is driven by a slide driving unit (notshown) so as to reciprocally move along the radius of the optical disk1.

[0136] The signal processing and controlling unit 35 implements varioussignal processing and controlling operations. For example, theillumination source 41 is controlled in terms of output power inread/write operations. The double-axis actuator 45 is controlled inresponse to the outputs of the focus error signal detecting element andthe tracking error signal detecting element, to control the focusing andtracking actions of the objective lens 44. The signal processing andcontrolling unit 35 further controls the slide driving unit and hencethe movement of the optical system unit 34 along the radius of theoptical disk 1. Thereby, the optical system unit 34, hence the objectivelens 44, is moves to a position where the unit 34 can read/write data ona predetermined track. Other control actions of the signal processingand controlling unit 35 will be described later.

[0137] In the optical-disk-read/write apparatus 31, the light beam 12 isconcentrated on either the first storage layer 10 or the second storagelayer 8 by the mechanism discussed in the foregoing, so that data isread/written from/into either the first storage layer 10 or the secondstorage layer 8 along the guiding groove 13.

[0138] In the present embodiment, in the optical-disk-read/writeapparatus 31, data is read/written from/into the second storage layer 8only after the recordable area 3 of the first storage layer 10 is fullyrecorded. Actions in this case are implemented by the signal processingand controlling unit 35 which controls the optical system unit(illuminating means) 34 and the slide driving unit (illuminating means).

[0139] Actions in this case are shown in FIG. 1. Referring to thatfigure, when the read/write light beam 12 is projected to the secondstorage layer 8, the recordable areas 3 of the first storage layer 10are fully recorded in advance (shown in black). Therefore, the lightbeam 12 is transmitted through the fully recorded, first storage layer10 and projected to the second storage layer 8.

[0140] Assuming the foregoing structure, the following will describe howthe optical-disk-read/write apparatus 31 reads/writes data on theoptical disk 1.

[0141] In the optical-disk-read/write apparatus 31, the light beam 12emitted by the illumination source 41 is collimated by the collimatorlens 42, transmitted through the beam splitter 43, before entering theobjective lens 44. Then, the light beam 12 is focused by the objectivelens 44 on either the first storage layer 10 or the second storage layer8 of the optical disk 1. The reflection from the optical disk 1 passesthrough the objective lens 44, deflected by the beam splitter 43, andfocused by the collective lens 46 on the light-receiving element 47.

[0142] Thereafter, based on the output of the light-receiving element47, the signal processing and controlling unit 35 controls thedouble-axis actuator 45 and hence the objective lens 44 for its precisefocusing and tracking actions. Thus, in the optical-disk-read/writeapparatus 31, to read/write data from/into either the first storagelayer 10 or the second storage layer 8, the light beam 12 is focused onthat storage layer along the guiding groove 13.

[0143] In the foregoing situation, the following will describe how theoptical-disk-read/write apparatus 31 reads/writes data on the opticaldisk 1, provided that data is recorded starting with the innermost part4 of the recordable area 3 of the first storage layer 10 of the opticaldisk 1 until data fills part of the recordable area 3 of the firststorage layer 10 and then the operation moves to reading/writing data inthe second storage layer 8. It is also supposed that the optical disk 1is a high-to-low medium such that the interval area is more reflectivethan the recording mark area and data is recorded by phase change.

[0144] As a result of recording in the first storage layer 10, as shownin FIGS. 6, 7, a recorded area 51 (shown by hatched lines) shown isproduced covering the innermost part 4 of the recordable area 3 of thefirst storage layer 10 up to partway of the recordable area 3.

[0145] Here, the first storage layer 10 is more optically transmissivein the recorded area 51 than other areas. As a result, the light beam 12projected on the second storage layer 8 is more intense when it isconcentrated on the second storage layer 8 if it has passed through therecorded area 51 than if it has passed through an area other than therecorded area 51 (a non-recorded area). In other words, in recordingdata into the second storage layer 8, the light beam 12 varies inintensity when it reaches the second storage layer 8 after passingthrough the first storage layer 10, depending on whether it has comethrough the recorded area 51. In this case, to record data into thesecond storage layer 8, a complex write system is required which canvary the light beam 12 in intensity depending on whether there are anyrecords stored in the first storage layer 10.

[0146] The same description applies to the case where data is read fromthe second storage layer 8, and a similarly complex read system isrequired, because the return light reflected off the second storagelayer 8 changes in quantity depending on whether the light beam 12 haspassed through the recorded area 51 of the first storage layer 10.

[0147] Accordingly, in the optical-disk-read/write apparatus 31 of thepresent embodiment, as shown in FIG. 1, data is read/written from/intothe second storage layer 8 only after the recordable area 3 of the firststorage layer 10 is fully recorded. In other words, to record data onthe optical disk 1, the optical-disk-read/write apparatus 31 firstwrites data in the first storage layer 10, and only after the recordablearea 3 of the first storage layer 10 is recorded to its full capacity,starts writing or reading data into/from the second storage layer 8.

[0148] The operation ensures that in the read/write operation as to thesecond storage layer 8, the light beam 12 projected on the secondstorage layer 8 always passes through the fully recorded, first storagelayer 10 before entering the second storage layer 8. In both read andwrite operations, the light beam 12 has a constant intensity when itreaches the second storage layer 8, which eliminates the need to use acomplex read/write system to control the intensity of the light beam 12.Stable read/write operations are thus achieved.

[0149] To carry out such operations, the signal processing andcontrolling unit 35 is provided with a write-start address producingcircuit 81 and an illuminating-unit-controlling circuit 82 as shown inFIG. 8. The illuminating unit controlled by theilluminating-unit-controlling circuit 82 is inclusive of, for example,the optical system unit 34 and the slide driving unit.

[0150] To write data on the optical disk 1, first, a recording statusmanaging signal is reproduced from data recorded in a recording statusmanaging area of the optical disk 1, and the signal is all recorded inthe write-start address producing circuit 81 in the signal processingand controlling unit 35. The recording status managing area is providedat a particular position in the first storage layer 10. The recordingstatus managing area may contain the title of the recorded material, aswell as an address representing a recording range.

[0151] Thereafter, the write-start address producing circuit 81 producesa write-start address for the optical disk 1, and theilluminating-unit-controlling circuit 82 controls focus and tracking soas to move the light beam spot to the write-start address. This actiontriggers recording in the recordable area 3 of the first storage layer10.

[0152] Thereafter, data is written to the first storage layer 10 to itsfull capacity, that is, until the last address of the first storagelayer 10 is detected. If data is written to the second storage layer 8without a break, the light beam 12 is concentrated on the second storagelayer 8 to similarly carry out recording in the recordable area 3 of thesecond storage layer 8.

EMBODIMENT 2

[0153] The following will describe another embodiment of the presentinvention in reference to FIGS. 9-11. An optical disk 61 of the presentembodiment is operational with the optical-disk-read/write apparatus 31which works as described in the foregoing.

[0154] The optical disk 61 of the present embodiment has extended areas62 in the innermost part 4 a and the outermost part 5 a of therecordable area 3 a of the first storage layer 10 as shown in FIGS. 9,10. Therefore, the innermost part 4 a of the first storage layer 10extends further inwards in relation to the diameter of the optical disk1 when compared to the innermost part 4 b of the second storage layer 8.The outermost part 5 a of the first storage layer 10 extends furtheroutwards in relation to the diameter when compared to the outermost part5 b of the second storage layer 8.

[0155] In other words, the recordable area 3 a of the first storagelayer 10 is greater than the recordable area 3 b of the second storagelayer 8 by the extended areas 62 in the innermost part 4 a and in theoutermost part 5 a. FIG. 9 is used to show the innermost parts 4 a, 4 band the outermost parts 5 a; 5 b for convenience.

[0156] No matter how large or small the extended areas 62 are, theirmere provision reduces the loss in intensity of a light beam projectedto the recordable area 3 b of the second storage layer 8 as will bedescribed later. To further and preferably reduce the loss in intensityof such a light beam, each extended area 62 should be specified enoughwide (or long when measured along a diameter of the optical disk 1) thatthe light beam 12 may not spill out of the recordable area 3 a,inclusive of the extended area 62, of the first storage layer 10regardless whether the light beam 12 is focused on the innermost part 4b or the outermost part 5 b of the recordable area 3 b of the secondstorage layer 8.

[0157]FIG. 11 shows an optical disk for comparison to explain thefunctions of the optical disk 61. In the optical disk 63, the recordablearea of the first storage layer 10 is as large as that of the secondstorage layer 8. The innermost part 4 and the outermost part 5 in thefirst storage layer 10 are positioned directly above and occupy the samearea as their equivalents of the second storage layer 8.

[0158] As shown in FIGS. 9, 11, in both optical disks 61, 63, the firststorage layer 10 and the second storage layer 8 each have a guidinggroove 13, and the first storage layer 10 is fully recorded along theguiding groove 13 up to either the innermost part 4 a, 4 or theoutermost part 5 a, 5 of the recordable area 3 a, 3. In the figures, thefully recorded status of the guiding groove 13 is shown by bold lines.In other words, in the readout/write on the optical disks 61, 63, theoptical-disk-read/write apparatus 31, again, first writes data in therecordable area 3 a, 3 of the first storage layer 10 to its fullcapacity before data is read/written in the recordable area 3 b, 3 ofthe second storage layer 8.

[0159] In the arrangement, as to the optical disk 63 equipped withrecordable areas 3 with no extended area 62 on the first storage layer10, the light beam 12 b projected on the recordable area 3 of the secondstorage layer 8 somewhere midway in relation to the radius of the diskto read/write data in the second storage layer 8 passes entirely throughthe recordable area (fully recorded area) 3 where the first storagelayer 10 exhibits a relatively high transmittance.

[0160] By contrast, the light beam 12 c, if projected close to theinnermost part 4 or the outermost part 5 of the second storage layer 8,does not entirely passes through the recordable area (fully recordedarea) 3 where the first storage layer 10 exhibits a relatively hightransmittance, but partially passes through unrecordable areas 64 otherthan the recordable area 3 where the first storage layer 10 exhibits arelatively lower transmittance. Accordingly, the light beam 12 c is lessintense than the light beam 12 b. Therefore, in reading/writing data inthe second storage layer 8, the light beam decreases, i.e., varies, inintensity in the innermost part 4, the outermost part 5, and theirneighborhoods of the recordable area 3 of the second storage layer 8,making it difficult to perform stable read/write operations across theentire recordable area 3 of the second storage layer 8.

[0161] By contrast, the optical disk 61 of the present embodiment isprovided with recordable areas 3 a with extended areas 62 on the firststorage layer 10. Thus, the light beam projected on the recordable area3 b of the second storage layer 8 to read/write data in the secondstorage layer 8 illuminates passes through the recordable area (fullyrecorded area) 3 a where the first storage layer 10 exhibits arelatively high transmittance not only when the light is directed on thesecond storage layer 8 somewhere midway in relation to the radius of thedisk, but also when the light is directed on the innermost part 4 b orthe outermost part 5 b of the second storage layer 8.

[0162] Thus, with the optical disk 61 of the present embodiment, thelight beam projected on the recordable area 3 b of the second storagelayer 8 always becomes the light beam 12 b which has passed through therecordable area (fully recorded) 3 a where the first storage layer 10exhibits a relatively high transmittance. The light beam does not varyin intensity whether data is read/written from/into any part of therecordable area 3 b of the second storage layer 8. Stable read/writeoperations are thus achieved.

[0163] To perform read/write operation on the second storage layer 8,the light beam 12 projected on the first storage layer 10 has a radiusnot exceeding the thickness of the guiding-groove-formed intermediatelayer 9. Therefore, the extended area 62 is sufficiently wide (or longwhen measured along a diameter of the optical disk) if it is as wide (orlong) as the guiding-groove-formed intermediate layer 9 is thick. If theguiding groove 13 on the first storage layer 10 is not concentric to theguiding groove 13 on the second storage layer 8, the extended area 62should be designed as wide as the guiding-groove-formed intermediatelayer 9 is thick, plus the deviation.

[0164]FIG. 9 is a schematic view, and the extended area 62 is shown aswide as the area covering two guiding grooves 13. However, in practice,the extended area 62 is as wide as the area covering at least 60 guidinggrooves 13, because the guiding grooves 13 have a pitch of about 0.3microns and the guiding-groove-formed intermediate layer 9 has athickness of about 20 microns.

[0165] In addition, the extended area 62 may be formed in only one ofthe innermost part 4 a and the outermost part 5 a of the first storagelayer 10, in which case the extended area 62 is functional as describedin the foregoing where it is formed.

EMBODIMENT 3

[0166] The following will describe a further embodiment of the presentinvention in reference to FIGS. 12-20. An optical disk 71 of the presentembodiment is operational with the optical-disk-read/write apparatus 31which works as described in the foregoing.

[0167] The optical disk 61 has an extended area 62 in the innermost part4 a and the outermost part 5 a of the recordable area 3 a of the firststorage layer 10. The optical disk 71 of the present embodiment has afully prerecorded pseudo-recording area 72 in an area which is anequivalent of the extended area 62 as shown in FIGS. 12, 13. Therefore,on the optical disk 71 of the present embodiment, the recordable area 3where ordinary information is recorded is as great on the first storagelayer 10 as it is on the second storage layer 8. The pseudo-recordingarea 72 may be provided before the optical disk 71 is shipped out, forexample.

[0168] In the arrangement, to perform normal read/write on the opticaldisk 71, similarly to the foregoing case, the optical-disk-read/writeapparatus 31 first writes data in the first storage layer 10, and onlyafter the recordable area 3 is recorded to its full capacity, startswriting or reading in recordable area 3 of the second storage layer 8,in which case, the pseudo-recording area 72 is already fully recorded.

[0169] As mentioned in the foregoing, the optical disk 71 of the presentembodiment has a pseudo-recording area 72 inside the innermost part 4 band outside the outermost part 5 b of the recordable area 3 of the firststorage layer 10 in relation to the diameter of the disk 71. Therefore,to perform read/write in the second storage layer 8, similarly to thecase of the optical disk 61, the light beam projected on the recordablearea 3 of the second storage layer 8 always becomes the light beam 12 bhaving passed through a fully recorded area where the first storagelayer 10 has a relatively high transmittance. The light beam does notvary in intensity whether data is read/written from/into any part of therecordable area 3 of the second storage layer 8. Stable read/writeoperations are thus achieved.

[0170] Further, unlike the optical disk 61, the optical disk 71 has therecordable area 3 which is as large on the first storage layer 10 as onthe second storage layer 8, and the guiding grooves 13 on the recordablearea 3 may share a common format. As a result, the optical system unit34 is controlled in terms of its position in performing read/write onthe first storage layer 10 in the same manner as in performingread/write on the second storage layer 8.

[0171] The pseudo-recording area 72 may be formed on the optical disk 61with an extended area 62, by the optical-disk-read/write apparatus 31recording data in that extended area 62 to the full capacity. Theoptical disk 71 can be thus made from an optical disk 61. In such anarrangement, it is not necessary to fabricate an optical disk 71 byforming a pseudo-recording area 72 on an optical disk 61 prior toshipment. The omission of the step allows for reduction of the cost ofthe optical disk 61 (71).

[0172] The optical-disk-read/write apparatus 31 forms a pseudo-recordingarea 72 by fully recording the extended area 62 prior to ordinaryrecording in the first storage layer 10, for example, when the opticaldisk 61 is loaded into the optical-disk-read/write apparatus 31. In thiscase, the optical-disk-read/write apparatus 31 first reads data from anextended area 62 of the loaded optical disk 61, and if the extended area62 is not fully recorded, records data in the area 62 to its fullcapacity. The process is controlled by the signal processing andcontrolling unit 35 of the optical-disk-read/write apparatus 31.

[0173] To implement such control, the signal processing and controllingunit 35 is provided with an extended-area-recording-status-checkingcircuit 83 and an illuminating-unit-controlling circuit 82 (detailed inthe foregoing) as shown in FIG. 14.

[0174] In the arrangement, as the optical disk 61 is loaded, theoptical-disk-read/write apparatus 31 first reads data from its extendedarea. The extended-area-recording-status-checking circuit 83 checksbased on a reproduction signal from the extended area 62 whether or notthe extended area 62 is fully recorded. If the check turns out that theextended area 62 is not fully recorded, theextended-area-recording-status-checking circuit 83 regards the loadedoptical disk 61 as being never used, and supplies anextended-area-writing-instruction signal to theilluminating-unit-controlling circuit 82 prior to the start of arecording action carried out on the first storage layer 10. Uponreceiving that signal, the illuminating-unit-controlling circuit 82controls the illuminating unit so as to make the extended area 62 on theoptical disk 61 fully recorded.

[0175] Meanwhile, if the check turns out that the extended area 62 isfully recorded, the extended-area-recording-status-checking circuit 83regards the loaded optical disk 61 as being already used, and supplies anormal writing-instruction signal to the illuminating-unit-controllingcircuit 82. Upon receiving that signal, theilluminating-unit-controlling circuit 82 controls the illuminating unitso as to perform an ordinary recording action on the optical disk 61.

[0176] The pseudo-recording area 72 may store absolutely nonsense ormeaningless information. Alternatively, if the optical disk 61 isprovided with the pseudo-recording area 72 before being shipped out, thepseudo-recording area 72 may contain a disk ID (identificationinformation) or encryption code information (encryption information)which match that particular optical disk 61, but not the other disks.

[0177] If the pseudo-recording area 72 contains encryption codeinformation, the optical-disk-read/write apparatus 31 may recordinformation in the recordable area 3 of the optical disk 71 only afterthe apparatus 31 encrypts the information based on the encryption codeinformation. In this case, to record information on the optical disk 71,the optical-disk-read/write apparatus 31 first reads the encryption codeinformation of pseudo-recording area 72 and encrypts information to berecorded, based on the encryption code information. In addition, toreproduce information from an encrypted optical disk 71, theoptical-disk-read/write apparatus 31 decrypts information after readoutfrom the recordable area 3. These processes are controlled by the signalprocessing and controlling unit 35.

[0178] In this case, the optical-disk-read/write apparatus 31 cannotdecrypt information which is read out from the optical disk 71 unlessthe apparatus 31 is equipped with a function to decrypt the encryptedinformation, which makes it possible to prevent the illegal copying andother uses of the optical disk 71.

[0179] As mentioned in the foregoing, to record information on theoptical disk 71 after encrypting it based on the encryption codeinformation in the pseudo-recording area 72, the signal processing andcontrolling unit 35 is provided with the encrypting circuit 84 and theilluminating-unit-controlling circuit 82 as shown in FIG. 15.

[0180] In the arrangement, prior to taking a recording action on theoptical disk 71, the encryption code information is reproduced which isrecorded in advance in the pseudo-recording area 72 of the optical disk71. The encrypting circuit 84 encrypts recording information based onthe encryption code information and supplies the encrypted recordinginformation to the illuminating-unit-controlling circuit 82. Theilluminating-unit-controlling circuit 82 controls the illuminating unitso that the recording information is recorded on the optical disk 71.

[0181] In addition, if the pseudo-recording area 72 contains diskidentification information, it is possible to prevent the illegalcopying and other uses of the optical disk 71 by managing the diskidentification information in the optical-disk-read/write apparatus 31or in a server or the like connected to the optical-disk-read/writeapparatus 31. The managing of the disk identification information refersto the processing to count the times the optical disk 71 is used tolimit the times the disk is used, for example.

[0182] In addition, provided that the pseudo-recording area alreadycontains disk identification information or encryption code information,designing the pseudo-recording area 72 as a read-only area prohibitsrewriting these sets of information. This further appropriately preventsthe illegal copying and other uses of the optical disk 71.

[0183] In addition, as mentioned earlier, when theoptical-disk-read/write apparatus 31 forms the pseudo-recording area 72on the optical disk 61 to form the optical disk 71 from the optical disk61, the optical-disk-read/write apparatus 31 may record, in thepseudo-recording area 72, the apparatus ID information which is uniqueto the optical-disk-read/write apparatus 31 or encryption codeinformation which is unique to the optical-disk-read/write apparatus 31.

[0184] When the optical-disk-read/write apparatus 31 records theapparatus ID information on the pseudo-recording area 72, the signalprocessing and controlling unit 35 in the optical-disk-read/writeapparatus 31 is equipped with anidentification-information-presence-checking circuit 85 and theilluminating-unit-controlling circuit 82 as shown in FIG. 16.

[0185] In the arrangement, as the optical disk 61 is loaded, theoptical-disk-read/write apparatus 31 first reads the extended area. Theidentification-information-presence-checking circuit 85 checks based ona reproduction signal from the extended area 62 whether the apparatus IDinformation is present in the extended area 62. If the check turns outthat the extended area 62 contains no apparatus ID information, theidentification-information-presence-checking circuit 85 regards theloaded optical disk 61 as being as being never used, and supplies anidentification-information-writing-instructing signal to theilluminating-unit-controlling circuit 82 prior to the start of arecording action on the first storage layer 10. Upon receiving thatsignal, the illuminating-unit-controlling circuit 82 controls theilluminating unit so as to record the apparatus ID information in theextended area 62 of the optical disk 61. The apparatus ID information iscontained in the signal processing and controlling unit (identificationinformation storing means) 35.

[0186] Meanwhile, if the check turns out that the extended area 62 holdsapparatus ID information, theidentification-information-presence-checking circuit 85 regards theloaded optical disk 61 as being already used, and supplies a normalread/write-instructing signal to the illuminating-unit-controllingcircuit 82. Upon receiving that signal, theilluminating-unit-controlling circuit 82 controls the illuminating unitso as to perform an ordinary read/write action on the optical disk 61.

[0187] In addition, to record encryption code information in thepseudo-recording area 72 using the optical-disk-read/write apparatus 31,the signal processing and controlling unit 35 in theoptical-disk-read/write apparatus 31 is equipped with anencryption-information-presence-checking circuit 86 and theilluminating-unit-controlling circuit 82 as shown in FIG. 17.

[0188] In the arrangement, as the optical disk 61 is loaded, theoptical-disk-read/write apparatus 31 first reads the extended area 62.The encryption-information-presence-checking circuit 86 checks based ona reproduction signal from the extended area 62 whether the encryptioncode information (encryption information) is present in the extendedarea 62. If the check turns out that the extended area 62 contains noencryption code information, theencryption-information-presence-checking circuit 86 regards the loadedoptical disk 61 as being never used, and supplies anencryption-information-reading signal to theilluminating-unit-controlling circuit 82 prior to the start of arecording action on the first storage layer 10. Upon receiving thesignal, the illuminating-unit-controlling circuit 82 controls theilluminating unit to record encryption code information in the extendedarea 62 of the optical disk 61. The encryption code information iscontained in the signal processing and controlling unit (encryptioninformation storing means) 35.

[0189] Meanwhile, if the check turns out that the extended area 62 holdsencryption code information, theencryption-information-presence-checking circuit 86 regards the loadedoptical disk 61 as being already used, and supplies an ordinaryread/write-instructing signal to the illuminating-unit-controllingcircuit 82. Upon receiving the signal, the illuminating-unit-controllingcircuit 82 controls the illuminating unit so as to perform an ordinaryread/write action on the optical disk 61.

[0190] In addition, as mentioned earlier, when theoptical-disk-read/write apparatus 31 records apparatus ID information orencryption code information in the pseudo-recording area 72 (extendedarea 62), an arrangement may be made so that only theoptical-disk-read/write apparatus 31 which did that recording canreproduce information from the recordable area 3 of the optical disk 71(61).

[0191] Processing in this case is done as below, for example. Supposingthat the pseudo-recording area 72 of the optical disk 71 holds apparatusID information, to read the optical disk 71, the optical-disk-read/writeapparatus 31 first reproduce the apparatus ID information from thepseudo-recording area 72 of the optical disk 71, and then reads datafrom the optical disk 71 only when the apparatus ID information readoutmatches the apparatus ID information of the optical-disk-read/writeapparatus 31 as a result of checking.

[0192] To realize these actions, the signal processing and controllingunit 35 is equipped with an identification-information-match-checkingcircuit 87 and the illuminating-unit-controlling circuit 82 as shown inFIG. 18.

[0193] In the arrangement, as the optical disk 71 is loaded, theoptical-disk-read/write apparatus 31 first reads the pseudo-recordingarea 72. The identification-information-match-checking circuit 87compares the apparatus ID information obtained from the reproductionsignal read out from the pseudo-recording area 72 with the apparatus IDinformation assigned to the optical-disk-read/write apparatus 31 tocheck whether the two sets of apparatus ID information match. If thecheck turns out that the two sets of apparatus ID information match eachother, a read/write-instructing signal is supplied to theilluminating-unit-controlling circuit 82. Upon receiving the signal, theilluminating-unit-controlling circuit 82 controls the illuminating unitso as to perform a read/write action on the optical disk 71.

[0194] Meanwhile, if the two sets of apparatus ID information does notmatch each other, the identification-information-match-checking circuit87 supplies an identification-information-match-display signalrepresenting the situation to the illuminating-unit-controlling circuit82. Upon receiving that signal, the illuminating-unit-controllingcircuit 82 causes a display unit (not shown) to display a notice to thatsituation, for example. In this case, no data is read nor written on theoptical disk 71.

[0195] In addition, if the recordable area 3 of the optical disk 71holds information which is encrypted based on encryption codeinformation, to read the optical disk 71, the optical-disk-read/writeapparatus 31 decrypts the information read out from the recordable area3 based on the encryption code information of theoptical-disk-read/write apparatus 31. The decryption is done, as shownin FIG. 19, in a decrypting circuit 88 in the signal processing andcontrolling unit 35. In these circumstances, the information read outfrom the recordable area 3 can be decrypted only when the encryptioncode information used with the optical disk 71 matches the encryptioncode information provided to the optical-disk-read/write apparatus 31.The arrangement enables prevention of copying, legal or illegal, of theoptical disk 71.

[0196] In addition, the extended area 62 of the optical disk 61 can beused as a test write area as follows.

[0197] For example, the most suitable light beam intensity to write dataon the optical disk 61, that is the most suitable writing power, variesdepending on changes in various factors including ambient temperature.Therefore, the optical-disk-read/write apparatus 31 usually test writesdata on the optical disk to calculate the most suitable writing power.Accordingly, on the optical disk 61, the extended area 62 is at leastpartly used as a test write area. The arrangement eliminates the need toseparately provide a test write area on the optical disk 61 and enablesefficient use of the recordable area 3 of the optical disk 61.

[0198] To implement these actions, the signal processing and controllingunit 35 is provided with a test-write-controlling circuit 89, awriting-power-checking circuit 90, and the illuminating-unit-controllingcircuit 82 as shown in FIG. 20.

[0199] In the arrangement, to write data on the optical disk 61, atest-write-recording instruction is given to the test-write-controllingcircuit 89 prior to writing in the first storage layer 10. Thus, theextended area 62 of the optical disk 61 is test written (recorded astest write). The test write is done with the writing power varied bylittle amounts.

[0200] Next, the data recorded in the test write is reproduced, and thereproduction signal is supplied to the writing-power-checking circuit90. The writing-power-checking circuit 90 determines the most suitablewriting power to record data on the optical disk 61 based on thereproduction signal. Thereafter, the information representative of themost suitable writing power is supplied to theilluminating-unit-controlling circuit 82 which controls the illuminatingunit so that data is written on the optical disk 61 using the mostsuitable writing power. The arrangement always enables recording underthe most suitable conditions regardless of changes in various factorsincluding ambient temperature and resultant changes in the recordingsensitivity of the optical disk 61.

[0201] Throughout the embodiments above, it was supposed that theoptical disks are all high-to-low phase change types of storage mediawhose interval areas have higher reflectance, i.e., lower transmittance,than the recording mark areas. The foregoing arrangements are howeverapplicable to those optical disks that may be low-to-high phase changetypes of storage media whose interval areas have lower reflectance,i.e., higher transmittance, than the recording mark areas.

EMBODIMENT 4

[0202] The following will describe another embodiment of the presentinvention in reference to FIGS. 21-25.

[0203] As shown in FIG. 23, an optical disk (optical storage medium) 101of the present embodiment has a center hole 102 at its center and arecordable area 103 outside the center hole 102 in relation to adiameter. The innermost part and the outermost part of the recordablearea 103 are shown by broken lines. The optical disk 101 employs alumped address scheme: an address area 104 is provided occupying apredetermined angular part of the recordable area 103, and addressinformation is represented by radially arranged address pit rows in theaddress area 104. In a non-address area 105, which is the part of therecordable area 103 other than the address area 104, there is provided aspiraling read/write guiding groove along which information can beread/written.

[0204] Like the optical disk 1, the optical disk 101 is arranged asshown in FIG. 3 and FIG. 4.

[0205]FIG. 21 shows an enlarged view of a part of the optical disk 101,where an address area 104 and non-address areas 105 adjacent to theaddress area 104 are depicted. Each non-address area 105 storesrecording marks 111 formed by projection of a light beam 12 along thespiraling guiding groove 13. The recording mark 111 differs fromsurrounding portions in optical transmittance.

[0206] In the address area 104, address tracks 113 made of address pits112 are provided to extend from the guiding grooves 13 in thenon-address areas 105. The address area 104 includes recorded areaswhere transmittance has changed and non-recorded areas wheretransmittance has not changed. Concretely, the (continuous) address area104 where transmittance has changed is formed by continuously recordingalternate address tracks 113 in relation to a diameter of the opticaldisk 101 by continuously projecting a light beam 12. In other words, oneof two address tracks 113 in the address area 104 which are adjacent inthe relation to a diameter of the optical disk 101 is continuouslyrecorded, whereas the other is unrecorded.

[0207] The optical-disk-read/write apparatus (optical read/writeapparatus) for reading/writing the optical disk 101 was alreadydescribed in reference to FIG. 5, as with the optical disk 1.

[0208] For the optical-disk-read/write apparatus 31 to read/write dataon the optical disk 101, the first storage layer 10 is read/written asshown in FIG. 22 by focusing and projecting the light beam 12 onto thefirst storage layer 10 while tracking the guiding groove 13 on the firststorage layer 10 and controlling the light beam intensity. In addition,the second storage layer 8 is read/written by focusing and projectingthe light beam 12 onto the second storage layer 8 while tracking theguiding groove 13 on the second storage layer 8 and controls the lightbeam intensity.

[0209] In this situation, it is supposed that the optical disk 101 is,for example, a high-to-low phase change type of storage medium in whichin the first storage layer 10 and the second storage layer 8, intervalareas between the recording marks 111 have a higher reflectance, i.e.,lower transmittance, than the recording marks 111.

[0210] In this case, in the non-address area 105 on the first storagelayer 10, the recording marks 111 have a higher transmittance.Therefore, referring to FIG. 22, the light beam 12 e projected onto thesecond storage layer 8 after passing trough a portion of the firststorage layer 10 where the recording marks 111 are present has a greaterintensity than the light beam projected onto the second storage layer 8without passing through that portion where the recording marks 111 arepresent. Likewise, since the address area 104 on the first storage layer10 has continuous storage areas 114, the light beam 12 f projected ontothe second storage layer 8 after passing through the address area 104has a greater intensity than the light beam projected onto the secondstorage layer 8 after passing through the address area in the case wherethere are no continuous storage areas 114. Therefore, as to the opticaldisk 101, the intensity of the light beam 12 f projected onto the secondstorage layer 8 after passing through an address area 104 on the firststorage layer 10 can be made closer to the intensity of the light beam12 e projected onto the second storage layer 8 after passing through thenon-address area 105 on the first storage layer 10.

[0211] As a result, as to the optical disk 101 employing a lumpedaddress scheme, the light beam intensity on the second storage layer 8can be retained at a substantially constant value regardless of whetherthe light is the light beam 12 e passing through the non-address area105 on the first storage layer 10 or the light beam 12 f passing throughthe address area 104 on the first storage layer 10, enabling stable anddesirable read/write on the second storage layer 8.

[0212] Besides, on the optical disk 101 of the present embodiment, acontinuous storage area 114 appears on alternate address tracks 113 inrelation to a diameter of the optical disk 101. Therefore, when thelight beam 12 is focused on the second storage layer 8 as shown in FIG.22, in the case where a beam spot 115 formed by the light beam 12 formson the first storage layer 10 as shown in FIG. 21, the sum of the areasof the recording marks 111 included in the area of the beam spot 115 inthe non-address area 105 on the first storage layer 10 is substantiallyequal to the sum of the continuous storage areas 114 included in thearea of the beam spot 115 in the address area 104. Thus, the intensityof the light beam 12 f projected onto the second storage layer 8 afterpassing through an address area 104 on the first storage layer 10 can bemade substantially equal to the intensity of the light beam 12 eprojected onto the second storage layer 8 after passing through thenon-address area 105 on the first storage layer 10.

[0213] In FIG. 21, ten address pits 112 are shown forming an addresstrack 113. However, FIG. 21 is only a schematic figure, and in practice,an address track 113 is made up of 1000 or more address pits 112 ofvarious lengths.

[0214] The continuous storage area 114 on the optical disk 101 may beformed prior to the shipment of the optical disk 101 or by theoptical-disk-read/write apparatus 31 based on reproduced addressinformation when the optical disk 101 is loaded in theoptical-disk-read/write apparatus 31. In the arrangement, the opticaldisk 101 does not need any particular arrangement that enables thedetermination whether to form a continuous storage area 114 in theaddress track 113.

[0215] To implement the actions, the signal processing and controllingunit 35 in the optical-disk-read/write apparatus 31 has arecorded/unrecorded switching circuit 121 and anilluminating-unit-controlling circuit 122 as shown in FIG. 24. Theilluminating unit controlled by the illuminating-unit-controllingcircuit 122 is inclusive of an optical system unit 34 and a slidedriving unit.

[0216] In the arrangement, the signal processing and controlling unit 35feeds a rotation synchronized signal produced in synchronism with therotation of the optical disk 101 to the recorded/unrecorded switchingcircuit 121. The recorded/unrecorded switching circuit 121 checks basedon the rotation synchronized signal for every turn of the optical disk101 whether to make the address track 113 a continuous storage area 114,that is, whether to continuously recorded the address track 113. Here,as mentioned earlier, the check is done so that alternate address tracks113 are continuous storage areas 114.

[0217] If the address track 113 is caused to be a continuous storagearea 114, the recorded/unrecorded switching circuit 121 feeds anaddress-track-continuous-recording-instructing signal to theilluminating-unit-controlling circuit 122. Upon receiving the signal,the illuminating-unit-controlling circuit 122 controls the illuminatingunit and continuously record the address track 113.

[0218] Meanwhile, if the address track is caused to be unrecorded, therecorded/unrecorded switching circuit 121 feeds anaddress-track-normal-reading-instructing signal to theilluminating-unit-controlling circuit 122. Upon receiving the signal,the illuminating-unit-controlling circuit 122 controls the illuminatingunit so as to read the address track 113 at a laser intensity which isincapable of recording data. In this case, address information isreproduced.

[0219] In addition, to implement the actions, the signal processing andcontrolling unit 35 in the optical-disk-read/write apparatus 31 mayinclude an arrangement shown in FIG. 25 which differs from thearrangement in FIG. 24. In that arrangement, the signal processing andcontrolling unit 35 has a subsequent-address-track-recorded/unrecordedchecking circuit 123 and the illuminating-unit-controlling circuit 122.

[0220] In this arrangement, thesubsequent-address-track-recorded/unrecorded checking circuit 123determines based on the address information obtained from the addressarea 104 whether to make the address track 113 a continuous storage area114. In other words, as mentioned in the foregoing, in the case wherealternate address tracks 113 are designated as continuous storage areas114, regardless whether to make the currently scanned address track 113a continuous storage area 114, that address track 113 is read first ofall, and it is determined based on the obtained address informationwhether to make a subsequent address track 113 a continuous storage area114.

[0221] In the arrangement, in the signal processing and controlling unit35, the illuminating-unit-controlling circuit 122 controls theilluminating unit so as to first read that address track 113 with whichthe process is started and obtain an address information reproductionsignal of the address track 113. The address information reproductionsignal is fed to the subsequent-address-track-recorded/unrecordedchecking circuit 123.

[0222] Upon receiving the address information reproduction signal, thesubsequent-address-track-recorded/unrecorded checking circuit 123 basedon that signal determines whether to make a subsequent address track acontinuous storage area 114.

[0223] If the subsequent address track 113 is to be continuouslyrecorded, the subsequent-address-track-recorded/unrecorded checkingcircuit 123 transmits asubsequent-address-track-continuous-recording-instructing signal to theilluminating-unit-controlling circuit 122. Upon receiving the signal,the illuminating-unit-controlling circuit 122 controls the illuminatingunit so as to make the subsequent address track 113 a continuous storagearea 114.

[0224] Meanwhile, if the subsequent address track 113 is to beunrecorded, the subsequent-address-track-recorded/unrecorded checkingcircuit 123 feeds a subsequent address-track-normal-reading-instructingsignal to the illuminating-unit-controlling circuit 122. Upon receivingthe signal, the illuminating-unit-controlling circuit 122 controls theilluminating unit so as to read the address track 113 at a laserintensity which is incapable of recording data.

[0225] In the arrangement in FIG. 24, if the process of forming acontinuous storage area 114 in the address area 104 is suspended beforecompletion and resumed again thereafter, it is unknown whether the lastaddress track 113 processed before the suspension is now a continuousstorage area 114 or not. Therefore, adjacent address tracks 113 arepossibly both continuous storage areas 114. In contrast, such situationsare prevented from happing in the arrangement in FIG. 25, the addressinformation is being always checked to determine whether to make thesubsequent address track 113 continuously recorded or unrecorded at all.

EMBODIMENT 5

[0226] The following will describe another embodiment of the presentinvention in reference to FIG. 26 and FIG. 27.

[0227] An optical disk 131 of the present embodiment has a judgementmark area 132 between a non-address area 105 and the head of an addressarea 104 as shown in FIG. 26 which is an enlarged view around the headof the address area 104.

[0228] In the judgement mark area 132 there are formed judgement pits(judgement marks) 133, 134 by which it is determined whether the addresstrack 113 in the address area 104 is made a continuous storage area 114or not. The judgement pits 133, 134 are located between the guidinggroove 13 in a non-address area 105 and its succeeding address track 113in the address area 104.

[0229] The judgement pits 133 show that the address tracks 113 are notto be made continuous storage areas 114 and are positioned in thejudgement mark area 132 near the non-address area 105. Meanwhile, thejudgement pits 134 show that the address tracks 113 are to be madecontinuous storage areas 114 and are positioned in the judgement markarea 132 near the address area 104. The judgement pits 133 exist atpositions shifted along the tracks when compared to the judgement pits134. In the present embodiment, as mentioned earlier, alternate addresstracks 113 are made continuous storage area 114; therefore, thejudgement pits 133, 134 appear alternately along a diameter of theoptical disk 131.

[0230] To appropriately make the address tracks 113 in the address area104 continuous storage areas 114 using the judgement pits 133, 134, thesignal processing and controlling unit 35 in the optical-disk-read/writeapparatus 31 is provided with a recorded/unrecorded-checking circuit 124and the illuminating-unit-controlling circuit 122 as shown in FIG. 27.

[0231] In the arrangement, upon detecting a judgement mark reproductionsignal which is a signal reproduced from the judgement pits 133, 134,the signal processing and controlling unit 35 feeds that signal to therecorded/unrecorded-checking circuit 124. Based on the judgement markreproduction signal, the recorded/unrecorded-checking circuit 124determines whether or not the address tracks 113 associated with thejudgement pits 133, 134 are to be made continuous storage areas 114.

[0232] To make an address track 113 a continuous storage area 114, therecorded/unrecorded-checking circuit 124 feeds anaddress-track-continuous-recording-instructing signal to theilluminating-unit-controlling circuit 122. Upon receiving the signal,the illuminating-unit-controlling circuit 122 controls the illuminatingunit so as to make the associated address track 113 a continuous storagearea 114.

[0233] Meanwhile, to not make an address track 113 a continuous storagearea 114 (to make the address track 13 unrecorded), therecorded/unrecorded-checking circuit 124 fees anaddress-track-normal-reading-instructing signal to theilluminating-unit-controlling circuit 122. Upon receiving the signal,the illuminating-unit-controlling circuit 122 controls the illuminatingunit so as to read the address track 113 at a laser intensity which isincapable of recording data.

[0234] As mentioned in the foregoing, as to the optical disk 131 of thepresent embodiment, it can be immediately determined owning to thejudgement pits 133, 134 in the judgement mark area 132 whether to makean address track 113 in the address area 104 a continuous storage area114. Therefore, the processing velocity of the optical-disk-read/writeapparatus 31 can be increased without reading the address track 113 inthe address area 104, i.e., address information.

EMBODIMENT 6

[0235] The following will describe another embodiment of the presentinvention in reference to FIGS. 28-31.

[0236] As shown in FIG. 28, an optical disk 141 of the presentembodiment is readable/writeable on both a groove 142 and a land 143which are formed alternately as viewed along a diameter of the opticaldisk 141 in the non-address area 105. The groove 142 and land 143 arespiral and recording marks 111 are formed on the groove 142 and land 143by projection of a light beam 12.

[0237] The address area 104 is made up of a first address area 144 and asecond address area 145 which are adjacent to each other along tracks.In the first address area 144 constituting a head part of the addressarea 104, there are formed first address pits 146 along imaginary linesextending from the groove 142. In the second address area 145constituting the tail part of the address area 104, there are formedsecond address pits 147 along imaginary lines extending from the land143. Relatively shifting the positions of the first address area 144 andthe second address area 145 along the tracks so that they do not overlapin a direction normal to the tracks eliminates crosstalk in signalsreproduced from the first and second address pits 146, 147. Thepositions of the first address area 144 and the second address area 145may be reversed.

[0238] In addition, some of the address tracks 113 in the address area104 extend from the groove 142, while the others extend from the land143. In the present embodiment, those address track 113 extending fromthe groove 142 are made continuous storage areas 114. In addition, theaddress track 113 is formed in both the first address area 144 and thesecond address area 145. Those address tracks 113 extending from thegroove 142 have the first address pits 146 in the first address area144, and those extending from the land 143 have the second address pits147 in the second address area 145.

[0239] As mentioned in the foregoing, as to an optical disk 141 of thepresent embodiment, continuous storage areas 114 are formed in thoseaddress tracks 113 extending from the groove 142, that is, in the firstaddress area 144 and the second address area 145 of the address track113. Therefore, like the foregoing optical disks 101, 131, to read/writethe second storage layer 8, the sum of the areas of the recording marks111 included in the area of the beam spot 115 in the non-address area105 on the first storage layer 10 is substantially equal to the sum ofthe continuous storage areas 114 included in the area of the beam spot115 in the address area 104.

[0240] Thus, the intensity of the light beam 12 f projected onto thesecond storage layer 8 after passing through an address area 104 on thefirst storage layer 10 can be made substantially equal to the intensityof the light beam 12 e projected onto the second storage layer 8 afterpassing through the non-address area 105 on the first storage layer 10.As a result, as to the optical disk 141 employing a lumped addressscheme, the light beam intensity on the second storage layer 8 can beretained at a substantially constant value regardless of whether thelight is the light beam 12 e passing through the non-address area 105 onthe first storage layer 10 or the light beam 12 f passing through theaddress area 104 on the first storage layer 10, enabling stable anddesirable read/write on the second storage layer 8.

[0241] In the present embodiment, the continuous storage area 114 issupposed to be formed in those address tracks 113 which extend from thegroove 142. The present embodiment is not limited by this: thecontinuous storage area 114 may be formed in those address tracks 113which extend from the land 143.

[0242] In addition, as in previous cases, the continuous storage area114 may be formed prior to the shipment of the optical disk 141 or byusing the optical-disk-read/write apparatus 31 after shipment. If theoptical-disk-read/write apparatus 31 is used to from an continuousstorage area 114, the aforementioned methods are all applicable.

[0243] Further, to form a continuous storage area 114, the signalprocessing and controlling unit 35 may have a land/groove determiningcircuit 125 and the illuminating-unit-controlling circuit 122 as shownin FIG. 29. In this arrangement, for example, it is determined whetherthe track currently being scanned is the groove 142 or the land 143, andthose address tracks 113 which extend from either the groove 142 or theland 143 in the address area 104 are made continuous storage areas 114according to a result of the determination.

[0244] In the arrangement, the land/groove determining circuit 125determines whether the track currently being scanned is the groove 142or the land 143 from a tracking servo signal or an address informationreproduction signal. If the determination turns out that it is thegroove 142, the land/groove determining circuit 125 feeds anaddress-track-continuous-recording-instructing signal to theilluminating-unit-controlling circuit 122 to make an address track 113 acontinuous storage area 114. Upon receiving the signal, theilluminating-unit-controlling circuit 122 controls the illuminating unitso as to make an address track 113 which extends from the groove 142 acontinuous storage area 114.

[0245] Meanwhile, if the determination turns out that it is the land143, the recorded/unrecorded-checking circuit 124 feeds anaddress-track-normal-reading-instructing signal to theilluminating-unit-controlling circuit 122. Upon receiving the signal,the illuminating-unit-controlling circuit 122 controls the illuminatingunit so as to read the address track 113 at a laser intensity which isincapable of recording data.

[0246] In addition, as to the optical disk 141, as shown in FIG. 30, thecontinuous storage area 114 may be formed in the second address area 145in those address tracks 113 which extend from the groove 142, in thefirst address area 144 in those address tracks 113 which extend from theland 143, and in each address track 113. The first address area 144 andthe second address area 145 may be reversed in position. Further, thecontinuous storage area 114 may be formed only at places where the firstaddress pit 146 and the second address pit 147 are provided, converselyto the formation places in FIG. 30.

[0247] In the arrangement, like the foregoing cases, the intensity ofthe light beam 12 f projected onto the second storage layer 8 afterpassing through an address area 104 on the first storage layer 10 can bemade substantially equal to the intensity of the light beam 12 eprojected onto the second storage layer 8 after passing through thenon-address area 105 on the first storage layer 10. As a result, as toan arrangement employing a lumped address scheme, the light beamintensity on the second storage layer 8 can be retained at asubstantially constant value, enabling stable and desirable read/writeon the second storage layer 8.

[0248] Likewise, the continuous storage area 114 may be formed inadvance, before the optical disk 141 is shipped or by using theoptical-disk-read/write apparatus 31 when the optical disk 141 is loadedinto the optical-disk-read/write apparatus 31. The aforementionedmethods are all applicable in these cases. For example, the continuousstorage area 114 may be formed based on reproduced address informationor whether the track being scanned is the groove 142 or the land 143.

[0249] To implement the actions, the signal processing and controllingunit 35 in the optical-disk-read/write apparatus 31 is equipped with,for example, an address-information-presence-checking circuit 126 andthe illuminating-unit-controlling circuit 122 as shown in FIG. 31.

[0250] In the arrangement, the signal processing and controlling unit 35feeds an address information signal reproduced from the address area 104to the address-information-presence-checking circuit 126 where theaddress-information-presence-checking circuit 126 determines whether theinput signal is carrying address information.

[0251] If the determination turns out that no address information ispresent, the address-information-presence-checking circuit 126 feeds anaddress-track-continuous-recording-instructing signal to theilluminating-unit-controlling circuit 122 to make an area where addressinformation is missing for the address track 113, that is, an area ofthe first address area 144 or the second address area 145, a continuousstorage area 114. Upon receiving that signal, theilluminating-unit-controlling circuit 122 controls the illuminating unitso as to form a continuous storage area 114 in an area where there is noaddress information for the address track 113.

[0252] Meanwhile, if address information is present, theaddress-information-presence-checking circuit 126 controls theilluminating unit and reads the address track 113 at a laser intensitywhich is incapable of recording data, so that no continuous storage area114 is formed in an area where address information is present for theaddress track 113.

[0253] In this and foregoing embodiments, if the optical-disk-read/writeapparatus 31 is used to form the continuous storage area 114 on anoptical disk, the cost of the optical disk can be reduced by reducingthe manufacturing steps of the optical disk.

[0254] In addition, in this and foregoing embodiments, the optical diskswere supposed to be high-to-low phase change types of storage media suchthat the interval areas between recording marks 111 exhibit a higherreflectance, i.e., a lower transmittance, than the recording mark 111 inthe first storage layer 10 and the second storage layer 8. The foregoingarrangements are applicable even when the optical disks are low-to-highphase change types of storage media such that the interval areas exhibita lower reflectance, i.e., a higher transmittance, than the recordingmarks 111.

EMBODIMENT 7

[0255] The following will describe an embodiment of the presentinvention in reference to FIG. 62 and FIG. 63.

[0256] Referring to FIG. 63, an optical disk (optical storage medium)201 of the present embodiment has a center hole 202 at its center and arecordable area 203 outside the center hole 202 in relation to adiameter. As shown in FIG. 35 and FIG. 36, in the recordable area 203, aspiral (or concentric) read/write guiding groove G is formed in aguiding-groove-and-pits-formed layer 212 and aguiding-groove-and-pits-formed intermediate layer 214 along whichinformation can be read/written. In addition, an innermost part 204 isformed around the center hole 202 and an outermost part 205 is formednear the circumference of the optical disk 201.

[0257] The optical disk 201 has prepit areas 206 made up of an innerprepit area 206 a and an outer prepit area 206 b. The inner prepit area206 a is provided adjacently outside the innermost part 204, and theouter prepit area 206 b is provided adjacently inside the outermost part205. As shown in FIG. 37, in the prepit area 206, pits P are arrangedforming a spiral (or concentric circles) in theguiding-groove-and-pits-formed layer 212 and theguiding-groove-and-pits-formed intermediate layer 214. Prepitinformation is read from the pit row of the pits P. In the pit row,typically, the writing power, reading power, and other kinds ofinformation on the optical disk 201 is prerecorded in the concave orconvex form (not shown) of the pits P.

[0258] As shown in FIG. 34 which is a vertical cross-sectional view ofthe optical disk 201, the optical disk 201 is structured from theguiding-groove-and-pits-formed layer 212, a second storage layer (lastdata storage layer) 213, the guiding-groove-and-pits-formed intermediatelayer 214, a first storage layer (light-striking-side storage layer)215, and a surface-coating layer 216, with the layers sequentiallystacked on a disk substrate 211. To read/write the first storage layer215 and the second storage layer 213 on the optical disk 201, a lightbeam 217 projected from one side of the disk, i.e., the side on whichthe surface-coating layer 216 exists, is concentrated on the first andsecond storage layers 215, 213.

[0259]FIG. 35 shows the arrangement of the optical disk 201 in moredetail. In FIG. 35, the disk substrate 211 is made of, for example, a1.2-mm thick, transparent polycarbonate substrate. Theguiding-groove-and-pits-formed layer 212 is made of, for example, a20-micron thick, ultraviolet-ray-setting resin layer and formed, forexample, by a pattern transfer technology termed 2P method. On one ofthe surfaces of the guiding-groove-and-pits-formed layer 212 which iscloser to the second storage layer 213, the guiding groove G is providedin the recordable area 203 and the pits P (not shown in FIG. 35) areprovided in the prepit area 206.

[0260] The second storage layer 213 includes, for example, an AlTi-alloyreflective film 213 a, a ZnS—SiO₂ interference film 213 b, a SiNprotective film 213 c, a GeSbTe phase change recording layer 213 d, aSiN protective film 213 e, and a ZnS—SiO₂ interference film 213 f. Thesefilms are formed as they are sequentially deposited on theguiding-groove-and-pits-formed layer 212 by means of sputtering.

[0261] Like the guiding-groove-and-pits-formed layer 212, theguiding-groove-and-pits-formed intermediate layer 214 is made of, forexample, a 20-micron thick, ultraviolet-ray-setting resin layer andformed by, for example, a pattern transfer technology termed 2P method.On one of the surfaces of the guiding-groove-and-pits-formedintermediate layer 214 which is closer to the first storage layer 215,the guiding groove G is provided in the recordable area 203 and the pitsP (not shown in FIG. 35) are provided in the prepit area 206.

[0262] Like the second storage layer 213, the first storage layer 215includes. for example, a ZnS—SiO₂ interference film 215 a, a SiNprotective film 215 b, a GeSbTe phase change recording layer 215 c, aSiN protective film 215 d and a ZnS—SiO₂ interference film 215 e. Thefirst storage layer 215 is formed by sequentially depositing these filmson the guiding-groove-and-pits-formed intermediate layer 214 by means ofsputtering.

[0263] The surface-coating layer 216 is made of, for example, a80-micron thick, ultraviolet-ray-setting resin layer, and formed by spincoating the first storage layer 215 with an ultraviolet-ray-settingresin and setting the resin by the projection of ultraviolet rays.

[0264] The optical disk substrate 211 is, as mentioned in the foregoing,a substrate made of a transparent polycarbonate. However, when a lightbeam 217 is incident to the surface-coating layer 216 as is the casewith the optical disk 201 of the present embodiment, the disk substrate211 does not need be transparent, and may be an opaque, metallicsubstrate.

[0265] In addition, the optical disk 201 of the present embodiment isprovided with the guiding-groove-and-pits-formed layer 212 and theguiding-groove-and-pits-formed intermediate layer 214 which are formedby 2P method and which have the guiding groove G and the pits P.However, a disk substrate 211 provided on its surface directly with aguiding groove G and pits P may be formed by, for example, injectionmolding. The structure including the disk substrate 211 does not requirethe guiding-groove-and-pits-formed layer 212 and theguiding-groove-and-pits-formed intermediate layer 214.

[0266] In addition, although the surface-coating layer 216 is formed onthe first storage layer 215 by spin coating, the layer 216 may beprovided instead in the form of uniformly thick, transparent sheetpasted on the first storage layer 215.

[0267] In addition, the optical disk 201 has a structure including theguiding-groove-and-pits-formed layer 212, the second storage layer 213,the guiding-groove-and-pits-formed intermediate layer 214, the firststorage layer 215, and the surface-coating layer 216 sequentiallystacked on the optical disk substrate 211. This is not the only optionavailable. For example, the optical disk 201 may be structured so thatit includes the guiding-groove-and-pits-formed layer 212, the firststorage layer 215, the guiding-groove-and-pits-formed intermediate layer214, the second storage layer 213, and the surface-coating layer 216sequentially stacked on the optical disk substrate 211, with the lightbeam 217 projected onto the optical disk substrate 211 as shown in FIG.38. In this structure, the films constituting the first storage layer215 and the second storage layer 213 are in the reverse order to thoseshown in FIG. 35.

[0268] An optical-disk-read/write apparatus (optical read/writeapparatus) which reads/writes on the optical disk 201 was, as with theoptical disk 1, described in reference to FIG. 5.

[0269] In the present embodiment, the optical-disk-read/write apparatus31 reads from, or writes into, the second storage layer 213 after therecordable area 203 of the first storage layer 215 is fully recorded.The operations in this case are carried out under the control of thesignal processing and controlling unit 35 on the optical system unit(illuminating means) 34 and the slide driving unit (illuminating means).

[0270] In the foregoing situation, the following will describe how theoptical-disk-read/write apparatus 31 reads/writes on the optical disk201, supposing that data, is recorded in the first storage layer 215 ofthe optical disk 201, starting with the inner prepit area 206 a in therecordable area 203 until data fills part of the recordable area 203 ofthe first storage layer 215, and then the operation moves toreading/writing in the second storage layer 213. It is also supposedthat the optical disk 201 is a high-to-low medium such that the intervalarea is more reflective than the recording mark area and data isrecorded by phase change.

[0271] As a result of recording in the first storage layer 215, as shownin FIG. 39 and FIG. 40, a recorded part 203 a 1 (shown by hatched lines)is produced covering the inner prepit area 206 a of the recordable area203 of the first storage layer 215 up to partway of the recordable area203.

[0272] Here, the first storage layer 215 is more optically transmissivethan in the recorded part 203 a 1 than other areas. As a result, thelight beam 217 projected on the second storage layer 213 is more intensewhen it is concentrated on the second storage layer 213 if the lightbeam 217 (light beam 217 b) has passed through the recorded part 203 a 1than if the light beam 217 (light beam 217 a) has passed through an areaother than the recorded part 203 a 1 (non-recorded area). In otherwords, in recording data into the second storage layer 213, the lightbeam 217 varies in intensity when it reaches the second storage layer213 after passing through the first storage layer 215, depending onwhether it has come through the recorded part 203 a 1. In this case, torecord data into the second storage layer 213, a complex write system isrequired which can vary the light beam 217 in intensity depending onwhether there are any records stored in the first storage layer 215.

[0273] A similar difference develops in intensity of the light beam 217,and a similarly complex read system is required when data is read fromthe second storage layer 213, because the return light reflected off thesecond storage layer 213 changes in quantity depending on whether thelight beam 217 has passed through the recorded part 203 a 1 of the firststorage layer 215.

[0274] Accordingly, in the optical-disk-read/write apparatus 31 of thepresent embodiment, as shown in FIG. 41, data is read/write from/intothe second storage layer 213 only after the recordable area 203 of thefirst storage layer 215 is fully recorded. In other words, to record onthe optical disk 201, the optical-disk-read/write apparatus 31 firstwrites data in the first storage layer 215, and only after therecordable area 203 of the first storage layer 215 is recorded to itsfull capacity, starts writing or reading data into/from the secondstorage layer 213.

[0275] The operation ensures that in the read/write operation as to thesecond storage layer 213, the light beam 217 projected on the secondstorage layer 213 always passes through the fully recorded, firststorage layer 215 before entering the second storage layer 213. In bothread and write operations, the light beam 217 has a constant intensitywhen it reaches the second storage layer 213, which eliminates the needto use a complex read/write system to control the intensity of the lightbeam 217. Stable read/write operations are thus achieved.

[0276]FIG. 62 shows the first storage layer 215 and the second storagelayer 213 near the periphery of the optical disk 201 in their initialstates. On the optical disk 201, the first storage layer 215 has anunrecorded recordable area 203 a and a blank area 205 a constituting theoutermost part 205, and the second storage layer 213 has an unrecordedrecordable area 203 b, an outer prepit area 206 a, and a blank area 205b constituting the outermost part 205. In this situation, the blankareas 205 a, 205 b are those areas where no guiding groove G or pits Pare formed. The innermost part 204 of the first and second storagelayers 215, 213 also has similar blank areas (not shown).

[0277] The optical disk 201 in this state exhibits uniformtransmittance, since the recordable area 203 aof the first storage layer215 is unrecorded. Therefore, when prepit information is reproduced byconcentrating the light beam 217 on the outer prepit area 206 b of thesecond storage layer 213, the intensity of the reproduction signal doesnot vary. In addition, since the prepit area 206 is provided to thesecond storage layer 213, the second storage layer 213 is stablyreadable/writeable without being affected by the prepit area 206.

[0278] Next, as shown in FIG. 42, writing in a part of the unrecordedrecordable area 203 a produces a recorded part 203 a 1 and leaves theother part as a non-recorded part 203 a 2. In this case, as shown inFIG. 43, in the recorded part 203 a 1, recording marks M with reducedtransmittance are formed in the guiding groove G. In the non-recordedpart 203 a 2, no recording marks M are formed and the transmittanceremains unchanged. Therefore, the light beam 217 c having passed throughthe recorded part 203 a 1 differs in intensity from the light beam 217 dhaving passed through the non-recorded part 203 a 2. The reproductionsignal of prepit information therefore differs in intensity between thelight beams 217 c and 217 d.

[0279] In addition, as to the optical disk 201, typically, it isimpossible to completely match the center of the spiral guiding groove Gon the first storage layer 215 and the center of the spiral pit row onthe second storage layer 213. Therefore, when the light beam 217 eilluminates both a part of the recorded part 203 a 1 and a part of thenon-recorded part 203 a 2 before being concentrated on the outer prepitarea 206 b of the second storage layer 213 as shown in FIG. 42, theboundary between the recorded part 203 a 1 and the non-recorded part 203a 2 moves in the light beam 217 e with the rotation of the optical disk.

[0280] Therefore, as shown in FIG. 44, the reproduction signal of theprepit information varies in intensity as the optical disk 201 rotates.FIG. 44 only shows the envelope E of the reproduction signal; theintensity of the reproduction signal is shown on the axis of ordinatesand the angular position of the rotating optical disk 201 is shown onthe axis of abscissas. FIG. 45 shows with the angle axis enlarged thereproduction signal S1 of prepit information at the 0-degree angularposition of FIG. 44 and the reproduction signal S2 of prepit informationat the 180-degree angular position of FIG. 44. To convert thereproduction signals S1, S2 into digital signals, detection needs tocarried out with the slice levels set to the mean levels to of thereproduction signals S1, S2. However, comparing the reproduction signalS1 with the reproduction signal S2 will show that the mean levels differgreatly, which makes it impossible to carry out detection using a singleslice level.

[0281] The problem can be solved by detecting the upper envelope E1 andlower envelope E2 which constitute the envelope E of the reproductionsignal and setting the variable slice level Lv to their mean levels asshown in FIG. 46. FIG. 47 shows the configuration of a reproductioncircuit producing a digital signal from the slice level Lv.

[0282] The reproduction circuit includes an envelope detecting circuit251, a slice level producing circuit 252, and a comparator 253.

[0283] The envelope detecting circuit 251 as envelope detecting means ismade of, for example, a peak-hold circuit and a bottom-hold circuit; thepeak-hold circuit detects the upper envelope E1 and the bottom-holdcircuit detects the lower envelope E2.

[0284] The slice level producing circuit 252 as mean level producingmeans produces a slice level Lv by outputting a mean value of values ofthe detected upper and lower envelopes E1, E2. The slice level producingcircuit 252 is made of, for example, an operation circuit including anadder circuit for adding the values of the envelopes E1, E2 and adivider circuit for dividing the sum by 2.

[0285] The comparator 253 as digital converting means compares thereproduction signal with the slice level Lv produced by the slice levelproducing circuit 252 and converts the reproduction signal to a binarydigital signal. For example, the comparator 253 produces a 1 for outputwhen the reproduction signal is above the slice level Lv and a 0 foroutput when the reproduction signal is below the slice level Lv.

[0286] In the reproduction circuit thus configured, the reproductionsignal is fed to the envelope detecting circuit 251 and the comparator253. The envelope detecting circuit 251 detects the upper envelopesignal E1 and the lower envelope E2 of the reproduction signal. Theslice level producing circuit 252 produces slice levels Lv from theenvelope E1, E2. The comparator 253 produces a digital signal bycomparing the reproduction signal with the slice level Lv.

[0287] In addition, FIG. 48 shows the relationship between thereproduction signal intensity and the angular position of the opticaldisk 201, as to the method to produce a digital signal from areproduction signal by means of the reproduction circuit shown in FIG.49. The reproduction circuit in FIG. 49 includes a high-pass filter 261,a slice level producing circuit 262, and a comparator 263.

[0288] The high-pass filter 261 as low frequency variation removingmeans removes low frequency variations from a reproduction signal andpasses high frequency components. The slice level producing circuit 262produces a slice level of a constant voltage. The comparator 263 asdigital converting means compares the reproduction signal transmittedthrough the high-pass filter 261 to the slice level as is the case withthe comparator 253 and converts into binary digital signal.

[0289] In the reproduction circuit thus configured, the incomingreproduction signal is first stripped of its low frequency variations bythe high-pass filter 261. The reproduction signal, before being fed tothe high-pass filter 261, includes low frequency variations, andtherefore the mean level of the envelope E changes as shown in FIG. 46.However, the reproduction signal is past through the high-pass filter261, and the mean level of the envelope E becomes constant regardless ofthe angle as shown in FIG. 48.

[0290] The comparator 263 compares the reproduction signal past throughthe high-pass filter 261 with the constant slice level Lc fed from theslice level producing circuit 262 and produces a digital signal.

[0291] Although the reproduction circuit and the slice level producingcircuit 262 produce the slice level Lc in the foregoing, the slice levelLc may be set to 0 volts, because the mean levels of the upper envelopeE1 and the lower envelope E2 are normally equal to 0 volts as thereproduction signal passes through the high-pass filter 261. Therefore,in this case, the slice level producing circuit 262 can be omitted.

[0292] As described in the foregoing, the provision of the prepit area206 in the second storage layer 213 enables the optical disk 201 toread/write data from/into the second storage layer 213 without changingthe read/write sensitivity of the recordable area 203. In addition, theuse of the reproduction circuit shown in FIG. 47 or FIG. 49 ensures thata digital signal is derived stably from a reproduction signal, even ifthe reproduction signal of prepit information varies in intensity withthe rotation of the optical disk 201 provided that the light beam 217 eilluminates both the recorded part 203 a 1 and the non-recorded part 203a 2 before being focused on the outer prepit area 206 b of the secondstorage layer 213.

[0293] However, as mentioned earlier, the non-recorded part 203 a 2exhibits a lower transmittance than the recorded part 203 a 1. When datais to be read from the prepit area 206 including the outer prepit area206 b using the light beam 217 d traveling through the non-recorded part203 a 2 of the first storage layer 215, as could be understood from FIG.46 and FIG. 48, the reproduction signal has so small an amplitude thatthe prepit information cannot be reproduced stably. Accordingly,preferably, the part of the first storage layer 215 through which thelight beam 217 e is transmitted is fully recorded and thus exhibits arelatively high transmittance.

[0294]FIG. 50 shows a structure of the optical disk 201 capable ofincreasing the amplitude of the reproduction signal obtained from prepitarea 206 (not shown except the outer prepit area 206 b) on the secondstorage layer 213.

[0295] The optical disk 201 has a pseudo-recording area 207 interposedbetween the recordable area 203 a and the blank area 205 a. Thepseudo-recording area 207 is provided in a part of the first storagelayer 215 which corresponds to the prepit area 206 of the first storagelayer 215 and stores pseudo information in advance. In thepseudo-recording area 207, as in the recordable area 203, thetransmittance lowers where recording marks M are formed in the guidinggroove G as shown in FIG. 51. Thus, the pseudo-recording area 207 has ashigh a transmittance as the recordable area 203, and the light beam 217passing through the pseudo-recording area 207 comes to have a highintensity. Thus, the amplitude of the reproduction signal of the prepitarea 206 on the second storage layer 213 can be increased.

[0296] The recording marks M formed on the pseudo-recording area 207differ from those formed on the recordable area 203; the former includeno main recording information, but pseudo recording information. Aspseudo recording information, no particular information needs berecorded, but nonsense or meaningless information may be recorded.Alternatively, if the pseudo-recording area 207 is to be formed inadvance prior to the shipment of the optical disk 201, identificationinformation, encryption information, and other kinds of information maybe recorded in the pseudo-recording area 207 which is unique toindividual optical disks 201.

[0297] In this situation, as shown in FIG. 50, preferably, thepseudo-recording area 207 is formed so that the light beams 217 f, 217 galways travel through the pseudo-recording area 207 of the first storagelayer 215 even when data is read from the edges of the prepit area 206 bof the second storage layer 213 in relation to the radius direction ofthe disk. Accordingly, the pseudo-recording area 207 is providedcovering a wider area than the outer prepit area 206 b of the secondstorage layer 213.

[0298] For example, supposing the first storage layer 215 is separatedfrom the second storage layer 213 by a distance of 20 microns, the lightbeam 217 focused on the second storage layer 213 forms on the firststorage layer 215 a spot having a radius of about 10 microns. Therefore,the pseudo-recording area 207 needs be formed at least about 10 micronswider than both ends of the prepit area 206 of the second storage layer213. In addition, when the center of the guiding groove G formed on thefirst storage layer 215 does not match the center of the pit row formedon the second storage layer 213, hence eccentricity exists between thetwo centers, the pseudo-recording area 207 needs be widened by an amountequivalent to the eccentricity. For this reason, the pseudo-recordingarea 207 is preferably formed about 100 microns wider than both ends ofthe prepit area 206 of the second storage layer 213.

[0299]FIG. 50 shows an example in which the pseudo-recording area 207 isprovided in the outer prepit area 206 b. A similar pseudo-recording areamay be provided in the inner prepit area 206 a too.

[0300] In this situation, the pseudo-recording area 207 may be eitherformed prior to the shipment of the optical disk 201 or formed by theoptical-disk-read/write apparatus 31 when an unused optical disk 201 isloaded in the optical-disk-read/write apparatus 31 for replay orrecording. The provision of the pseudo-recording area 207 using anoptical-disk-read/write apparatus eliminates the need to provide thepseudo-recording area 207 prior to the shipment of the optical disk,which enables reduction of the cost of the optical disk.

[0301]FIG. 52 shows a configuration of pseudo recording circuit providedin the optical-disk-read/write apparatus 31 to form a pseudo-recordingarea 207. The configuration includes the aforementionedpseudo-recording-status-checking circuit 271 in the signal processingand controlling unit 35.

[0302] The pseudo-recording-status-checking circuit 271 as recordingstatus checking means checks, based on the reproduction signal producedby a light-receiving element 47 from the reflection off thepseudo-recording area 207, whether the pseudo-recording area 207 alreadycontains pseudo recording information. Thepseudo-recording-status-checking circuit 271 includes a comparator andother circuits to check and determine whether the pseudo-recording area207 contains any records, in accordance with whether or not thereproduction signal which represents the quantity of light reflected offthe pseudo-recording area 207 exceeds a predetermined threshold value.

[0303] In the arrangement, the pseudo-recording area 207 is readimmediately after the optical disk 201 is loaded in theoptical-disk-read/write apparatus 31. Thepseudo-recording-status-checking circuit 271 checks based on thereproduction signal whether the pseudo-recording area 207 is fullyrecorded or not.

[0304] If the pseudo-recording area 207 is not fully recorded, thepseudo-recording-status-checking circuit 271 regards the optical disk201 as being never used, and feeds a pseudo writing-instruction signalto the illuminating-unit-controlling circuit 36 as pseudo-recordingmeans provided in the signal processing and controlling unit 35. As aresult, pseudo information is recorded in the pseudo-recording area 207of the first storage layer 215 under the control of theilluminating-unit-controlling circuit 36. Meanwhile, if thepseudo-recording area 207 is fully recorded, thepseudo-recording-status-checking circuit 271 regards the loaded opticaldisk 201 as having been used, and feeds an ordinary writing-instructionsignal to the illuminating-unit-controlling circuit 36. As a result, anordinary recording operation is performed as to the optical disk 201under the control of the illuminating-unit-controlling circuit 36.

[0305] Next, the following description will describe an optical disk 201in which the first storage layer 215 has a prepit area 206. As acomparative example, an optical disk 281 is first described with whichno consideration is given to the read/write sensitivity of the secondstorage layer 215.

[0306] With the optical disk 281, as shown in FIG. 53, a blank area 205a of the first storage layer 215 is provided in the same range as ablank area 205 b of the second storage layer 213. In the first storagelayer 215, an outer prepit area 206 b is provided between the recordablearea 203 a and the blank area 205 a. In addition, an inner prepit area206 a (not shown) is also provided on the first storage layer 215.

[0307] Since the prepit area 206 is located on the light-striking sideof the optical disk 281 thus structured, the reproduction signal derivedfrom the prepit area 206 never varies in intensity. The optical disk 281is free from the problem that the reproduction signal derived from theprepit area 206 varies in intensity as shown in FIG. 42. However, theprovision of the prepit area 206 on the first storage layer 215 causesthe same problem as with the conventional optical disk (see FIG. 70).Concretely, the first storage layer 611 exhibits different opticaltransmittances between the recordable area 603 and the prepit area 606,resulting in variations in read/write sensitivity of the second storagelayer 612. Now, the variations in recording sensitivity of the opticaldisk 281 are elaborately described.

[0308] As to the optical disk 281, the recordable area 203 a of thefirst storage layer 215 is first fully recorded by a recording operationof the optical-disk-read/write apparatus 31. In this situation, thefully recorded, recordable area 203 a includes high-transmittancerecording marks M, and the light beam 217 h concentrated on the secondstorage layer 213 after passing through the recordable area 203 aexhibits a relatively high intensity. Meanwhile, the light beam 217 iconcentrated on the second storage layer 213 after passing through theprepit area 206 with no recording marks M exhibits a relatively lowintensity.

[0309] Next, to record data in the recordable area 203 b of the secondstorage layer 213, the light beam 217 h and the light beam 217 i,although originally of the same intensity, differs in intensity whenthey reach the second storage layer 213. Therefore, the recordingsensitivity varies depending upon where recording takes place, whichmakes it extremely difficult to perform stable recording. Further, if alight beam passes through a boundary between the fully recordedrecordable area 203 a and the prepit area 206 before concentrated on thesecond storage layer 213, since there exists eccentricity which isdefined as the displacement in position between the center of theguiding groove G on the first storage layer 215 and the center of theguiding groove G on the second storage layer 213, the recordingsensitivity undesirably varies with rotation of the optical disk 281.

[0310] By contrast, the optical disk 201 shown in FIG. 54 provides meansto solve these problems by expanding the blank area 205 b. The followingwill describe such an optical disk 201.

[0311] As to the optical disk 201 shown in FIG. 54, the blank area 205 bthe second storage layer 213 is expanded inwards, and a light beam 217 jentering the optical disk 201 always passes through the fully recordedrecordable area 203 a of the first storage layer 215 before concentratedon the second storage layer 213. In this manner, as to the optical disk201, the recordable area 203 a of the first storage layer 215 is formedwider than the recordable area 203 b of the second storage layer 213,and the prepit area 206 is formed along the outer circumference of therecordable area 203 a. The configuration makes the intensity of thelight beam 217 j always constant on the second storage layer 213 andthus achieves stable recording to the second storage layer 213 andstable reproduction of prepit information from the first storage layer215.

[0312] Now, it will be described how much wider the recordable area 203a of the first storage layer 215 should be than the recordable area 203b of the second storage layer 213. Assuming that the first storage layer215 is separated from the second storage layer 213 by a distance of 20microns, the light beam 217 j focused on the second storage layer 213forms on the first storage layer 215 a spot having a radius of about 10microns. Therefore, the recordable area 203 b needs be formed at leastabout 10 microns wider than the width of the recordable area 203 a. Inaddition, when the center of the guiding groove G formed on the firststorage layer 215 does not match the center of the guiding groove Gformed on the second storage layer 213, hence eccentricity existsbetween the two centers, the recordable area 203 a needs be widened byan amount equivalent to the eccentricity. Therefore, in this case, therecordable area 203 a is preferably formed about 100 microns wider thanthe width of the recordable area 203 b.

[0313] As to the optical disk 201, the recordable area 203 b of thesecond storage layer 213 narrows down and the storage capacitydecreases. By contrast, the optical disk 201 shown in FIG. 55 and FIG.56 has such a structure to add to the storage capacity while preventingthe prepit area 206 from reducing the recording sensitivity.

[0314] The optical disk 201 has in place of the aforementioned prepitarea 206 a prepit area 208 made of an inner prepit area 208 a and anouter prepit area 208 b, as shown in FIG. 55. The prepit area 208 has anoptical transmittance which is equal to that of the fully recordedrecordable area 203 a of the first storage layer 215 shown in FIG. 56.

[0315] As shown in FIG. 57, in the prepit area 208, alternate pit rowsof pits P which are spirally (or concentrically) arranged have acontinuously recorded, continuous storage area R. In the continuousstorage area R, the pits P and the intervals between the pits P arecontinuously in the same state, i.e., have the same transmittance, asthe recording marks M in the recordable area 203 a.

[0316] In the recorded recordable area 203 a, a fully recorded portion(recording mark M) and a non-fully-recorded portions are formedalternately in the guiding groove G. In practice, the lengths of thefully recorded and non-fully-recorded portions along the guiding grooveG alters depending on recording information. However, as to the guidinggroove G, recording is done so that the recorded portions and thenon-fully-recorded portions are formed at a substantially equal ratio.In addition, the depression area (land area) between any adjacentguiding grooves G are non-recorded areas and formed substantially aswide as the guiding groove G. Therefore, the sum of the areas of therecording marks M is equal to ¼ the net area of the recordable area 203a.

[0317] Meanwhile, in the prepit area 208, the non-recorded area betweenany adjacent pit rows is formed substantially as wide as the diameter ofthe pit P. Therefore, to form a recorded portion (¼ the net prepit area208) which has an area substantially equal to the recorded portion ofthe recordable area 203 a, recording needs be done so that a continuousstorage area R can be formed for alternate pit rows.

[0318] Other than guiding groove recording schemes, to employ a land andgroove recording scheme whereby recording marks M are formed not only inthe guiding groove G, but also in land areas, the sum of the areas ofthe recording marks M formed in the recordable area 203 a is ½ the netarea of the recordable area 203 a. Therefore, to form a recorded portionhaving an area substantially equal to the recorded portion (½ the netarea of the prepit area 208) of the recordable area 203 a, recordingneeds be done so that a continuous storage area R can be formedcontinuously along a pit row.

[0319] As mentioned in the foregoing, the continuous storage area Rexhibits as high an optical transmittance as the recording mark M.Therefore, as shown in FIG. 58, the fully recorded portions formed onthe first storage layer 15 in the spots of a light beam 217 k passingthrough the fully recorded recordable area 203 a before beingconcentrated on the second storage layer 213 and a light beam 2171passing through the outer prepit area 208 b before being concentrated onthe second storage layer 213 have the substantially equal areas. Thismakes the intensities of the light beams 217 k, 217 l on the secondstorage layer 213 substantially equal, and the second storage layer 213no longer varies in recording sensitivity even when the prepit area 208is provided. Therefore, expanding the recordable area 203 b of thesecond storage layer 213 adds to the storage capacity as compared to theoptical disk 201 in FIG. 54.

[0320] In this situation, the blank areas 205 a, 205 b are unrecordedand exhibit low optical transmittance. The ends of the recordable area203 b of the second storage layer 213 therefore need be determined sothat the light beam 2171 reaching the second storage layer 213 alwayspasses through the outer prepit area 208 b, as shown in FIG. 56.

[0321] In this manner, as to the optical disk 201, in the prepit area208 of the first storage layer 215, alternate pit rows have a continuousstorage area R, and the outer periphery of the outer prepit area 208 bis positioned further outside the outer periphery of the recordable area203 b of the second storage layer 213. In the case of the inner prepitarea 208 a, its inner periphery is positioned further inside the innerperiphery of the recordable area 203 b of the second storage layer 213.Thus, the light beams 217 k, 217 l always have equal intensities on thesecond storage layer 213. Therefore, data is stably written to thesecond storage layer 213, and the optical disk 201 comes to have afurther increased capacity.

[0322] Now, it will be described how much closer to the outer peripherythe periphery of the outer prepit area 208 b should be positioned thanthe recordable area 203 b. Assuming that the first storage layer 215 isseparated from the second storage layer 213 by a distance of 20 microns,the light beam focused on the second storage layer 213 forms on thefirst storage layer 215 a spot having a radius of about 10 microns.Therefore, the outer prepit area 208 b needs be formed so that itsperiphery is positioned at least about 10 microns closer to the outerperiphery than the periphery of the recordable area 203 b. Likewise, theinner prepit area 208 a needs be formed so that its periphery ispositioned at least about 10 microns closer to the inner periphery thanthe periphery of the recordable area 203 b.

[0323] Further, if the center of the guiding groove G on the firststorage layer 215 does not match the center of the guiding groove G onthe second storage layer 213, and hence eccentricity exists, the outerprepit area 208 b needs be expanded by an amount equivalent to theeccentricity. In this case, the outer prepit area 208 b is preferablyformed so that its edges are positioned about 100 microns closer to theouter periphery than the edges of the recordable area 203 b. Preferably,the inner prepit area 208 a is formed likewise.

[0324] In this situation, the continuous storage area R may be formed inthe pit row in the prepit area 208 either prior to the shipment of theoptical disk 201 or by using the optical-disk-read/write apparatus 31when an unused optical disk 201 is loaded into theoptical-disk-read/write apparatus 31. The formation of the continuousstorage area R using the optical-disk-read/write apparatus 31 eliminatesthe need to form the continuous storage area R prior to the shipment ofthe optical disk 201, and reduces the cost of the optical disk 201.

[0325]FIG. 59 shows a configuration to form a continuous storage area Rin the pit row in the prepit area 208 using the optical-disk-read/writeapparatus 31 in the foregoing manner. The configuration includes theaforementioned continuous-storage-area-presence-checking circuit 291provided in the signal processing and controlling unit 35.

[0326] The continuous-storage-area-presence-checking circuit 291 ascontinuous storage area checking means checks and determines based onthe reproduction signal produced by the light-receiving element 47 fromthe reflection off the prepit area 208 whether the prepit area 208contains a continuous storage area R as mentioned in the foregoing. Thecontinuous-storage-area-presence-checking circuit 291 includes acomparator and other circuits to check and determine whether thepseudo-recording area 207 contains any records, in accordance withwhether or not the reproduction signal which represents the quantity ofreflected light reflected off the prepit area 208 exceeds apredetermined threshold value.

[0327] In the arrangement, to check the presence of the continuousstorage area R, the prepit area 208 is read immediately after theoptical disk 201 is loaded in the optical-disk-read/write apparatus 31.Here, a light beam is projected on the prepit area 208 for trackingunder the control of the illuminating-unit-controlling circuit 36 in thesignal processing and controlling unit 35. Here, the pit row acts as atracking guide which is a rough equivalent to the guiding groove G.

[0328] When there is already formed a continuous storage area R, thequantity of light reflected off the prepit area 208 changes foralternate pit rows, and the reproduction signal representative of thequantity of reflected light varies accordingly. In thecontinuous-storage-area-presence-checking circuit 291, as mentioned inthe foregoing, the varying reproduction signal is converted to a signalof a constant level by a low-pass filter and compared with apredetermined reference value by the comparator. In this case, thesignal is larger than the reference value, thecontinuous-storage-area-presence-checking circuit 291 regards the loadedoptical disk 201 as having been used and feeds an ordinarywriting-instruction signal to the illuminating-unit-controlling circuit36. As a result, under the control of the illuminating-unit-controllingcircuit 36, ordinary recording takes place on the optical disk 201.

[0329] Meanwhile, when there is formed no continuous storage area R, thequantity of light reflected off the prepit area 208 does not vary.Neither does the reproduction signal. Therefore, the signal havingpassed through the low-pass filter is smaller than the reference value,the continuous-storage-area-presence-checking circuit 291 regards theloaded optical disk 201 as being never used, and feeds acontinuous-recording-instructing signal to theilluminating-unit-controlling circuit 36 as continuous recording means.As a result, under the control of the illuminating-unit-controllingcircuit 36, recording takes place on the optical disk 201 so that acontinuous storage area R is formed in the prepit area 208.

[0330] So far, the description was limited only to the optical disk 201with only two data storage layers. Instead, the optical disk 201 mayinclude three or more data storage layers. The following will describesuch an optical disk 201 with three data storage layers.

[0331] In addition to a first storage layer 215 and a second storagelayer 213, the optical disk 201 includes a third storage layer 218 as alast data storage layer which is most distanced from a light-enteringsurface, as shown in FIG. 60. The prepit area 206 is provided not in thefirst storage layer 215 or the second storage layer 213, but only in thethird storage layer 218, between a recordable area 203 c and a blankarea 205 c.

[0332] As to the optical disk 201, similarly to the optical disk 201shown in FIG. 62, in reading data from a prepit area 206 in the thirdstorage layer 218. the quantity of light reflected off a prepit area 206varies depending upon whether the first storage layer 215 and the secondstorage layer 213 through which light beams 217 m, 217 n pass are fullyrecorded or not. However, a slice level can be produced from theenvelope of a reproduction signal by using the reproduction circuitshown in FIG. 47. Obtaining a digital signal with the slice level as areference, prepit information can be reproduced stably. In addition, byusing the reproduction circuit shown in FIG. 49, prepit information canbe reproduced stably by obtaining a digital signal by comparing with aconstant slice level a reproduction signal of the prepit area 206 fromwhich low frequency components are removed by a high-pass filter.

[0333] In this situation, in recording data on the optical disk 201, therecording on the second storage layer 213 is started after the firststorage layer 215 is fully recorded, and the recording on the thirdstorage layer 218 is started after the second storage layer 213 is fullyrecorded. In addition, in focusing a light beam on the second storagelayer 213, the light beam needs always be transmitted through a recordedarea 203 a of the first storage layer 215 so that a light beam ofconstant intensity reaches the second storage layer 213. To this end,the recordable area 203 a is formed wider than the recordable area 203 bboth on the inner and outer peripheries.

[0334] Next, as to the optical disk 201 shown in FIG. 61, the thirdstorage layer 218 has the prepit area 206, and the first storage layer215 and the second storage layer 213 have respective pseudo-recordingareas 207 a, 207 b where pseudo information is recorded. As to theoptical disk 201, the pseudo-recording areas 207 a, 207 b are formed atsuch positions that the light beams 217 m, 217 l focused on the prepitarea 206 of the third storage layer 218 are always transmitted throughthe pseudo-recording areas 207 a, 207 b before reaching the prepit area206.

[0335] Using such an optical disk 201, similarly to the optical disk 201shown in FIG. 50, due to relatively high optical transmittance of thepseudo-recording area 207 a, 207 b, the intensities of the light beams217 m, 217 n passing through the pseudo-recording areas 207 a, 207 b canbe maintained at high values. Therefore, it becomes possible to increasethe amplitude of the reproduction signal derived from the prepit area206 of the third storage layer 218 and eliminate the variations of thereproduction signal along the direction of the circumference.

[0336] The pseudo-recording areas 207 a, 207 b may be formed prior tothe shipment of the optical disk 201 or using theoptical-disk-read/write apparatus 31 in the aforementioned manner.

[0337] Further, the optical disk 201 shown in FIG. 62 has the prepitarea 206 only in the first storage layer 215 which is located close tothe light-entering surface. Such an optical disk 201, since the prepitarea 206 is located close to the light-entering surface, is free fromvariations in the quantity of light reflected off the prepit area 206and its prepit information can be stably reproduced.

[0338] In addition, to eliminate variations from recording sensitivity,similarly to the case in FIG. 54, in reading or writing in therecordable area 203 b of the second storage layer 213, a light beam 217o needs to always pass through a fully recorded recordable area 203 a ofthe first storage layer 215 before reaching the second storage layer213; and in reading or writing in the third storage layer 218, a lightbeam 217 p needs to always pass through the fully recorded recordableareas 203 a, 203 b of the first storage layer 215 and the second storagelayer 213, respectively, before reaching the third storage layer 218. Tothis end, the recordable area 203 b is formed wider than the recordablearea 203 c and the recordable area 203 a is formed wider than therecordable area 203 b.

[0339] The optical disk 201 shown in FIG. 63 has the prepit area 208(only the outer prepit area 208 b is shown in place of the prepit area206 in the first storage layer 215 of the optical disk 201 shown in FIG.62. The optical disk 201, similarly to the optical disk 201 in FIG. 56,has: the prepit area 208 where the optical transmittance is high; theinner prepit area 208 a whose inner edge is positioned further inwardsthan the inner edges of the recordable areas 203 b, 203 c; and the outerprepit area 208 b whose outer edge is positioned further outwards thanthe outer edges of the recordable areas 203 b, 203 c.

[0340] This makes always constant the intensities of a light beam 217 rreaching the second storage layer 213 and the light beam 217 s reachingthe third storage layer 218. Therefore, it data is recorded stably inthe second storage layer 213 and the third storage layer 218, and theoptical disk 201 is more capacious.

[0341] As described in the foregoing, an optical read/write apparatus ofthe present invention causes a read/write light beam from anilluminating section to strike only one side of an optical storagemedium including stacked data storage layers each of which isreadable/writeable separately from the other layers, and the apparatusincludes a controlling section for controlling the illuminating sectionso that data is read/written from/into a recordable area of a seconddata storage layer after a recordable area of a first data storage layeris fully recorded, and the first data storage layer is one of the datastorage layers which is located closest to a light-striking surface ofthe medium, and the second data storage layer is another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface.

[0342] Further, an optical read/write method of the present inventioncauses a read/write light beam to strike only one side of an opticalstorage medium including stacked data storage layers each of which isreadable/writeable separately from the other layers, and the methodincludes the step of reading/writing data from/into a second datastorage layer after fully recording a recordable area of a first datastorage layers which is located closest to a light-striking surface ofthe medium, and the second data storage layer is another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface.

[0343] According to the arrangement, after fully recording therecordable area of the first data storage layer on the light-strikingside, data is read/written from/into the second data storage layer whichis located next to the first data storage layer, opposite thelight-striking surface.

[0344] Therefore, when data is read/written from/into the second datastorage layer, substantially all the read/write light striking thesecond data storage layer after passing through the first data storagelayer passes through the recordable area of the first data storage layerthat has been recorded. Thus, even when an optical transmittance in therecordable area of the first data storage layer varies depending onwhether the recordable area holds any record or not, it is possible toilluminate light having uniform intensity to the substantially entirerecordable area of the second data storage layer. As a result, it ispossible to realize a desirable reading/writing property without using acomplex read/write system.

[0345] An optical read/write apparatus of the present invention causes aread/write light beam from illuminating means to strike only one side ofthe optical storage medium and is arranged so as to include controllingmeans for controlling the illuminating means so that an extended area isfully recorded prior to recording in an area other than the extendedarea in a recordable area in a first data storage layer of the opticalstorage medium.

[0346] In addition, an optical read/write method of the presentinvention is arranged to include the steps of preparing an opticalstorage medium and fully recording an extended area prior to recordingin an area other than the extended area in a recordable area in a firstdata storage layer of the optical storage medium.

[0347] According to the arrangement, since an optical storage medium isused which has an extended area in a recordable area of a first datastorage layer, as mentioned earlier, light can be projected at uniformintensity on substantially all recordable areas of the second datastorage layer. Therefore, desirable read/write characteristics can beimparted without using a complex read/write system.

[0348] In addition, the area other than the extended area in therecordable area of the first data storage layer is as large as arecordable area in a second data storage layer. The position of theilluminating means relative to the optical storage medium can becontrolled in the same manner with respect to read/write in the areaother than the extended area in the recordable area of the first datastorage layer and with respect to read/write in the recordable area ofthe second data storage layer.

[0349] An optical read/write apparatus of the present invention causes aread/write light beam from illuminating means to strike only one side ofan optical storage medium and is arranged so as to include:identification information storing means for storing identificationinformation which is unique to the optical read/write apparatus and bywhich the optical read/write apparatus is distinguished from otheroptical read/write apparatuses; and controlling means for controllingthe illuminating means so that the optical storage medium holds theidentification information in an extended area.

[0350] In addition, an optical read/write method of the presentinvention is arranged to include the steps of preparing the opticalstorage medium and storing in an extended area identificationinformation which is unique to an individual optical read/writeapparatus capable of reading/writing on the optical storage medium andby which the optical read/write apparatus is distinguished from otheroptical read/write apparatuses.

[0351] According to the arrangement, an optical storage medium can storein its extended area identification information by which the opticalread/write apparatus having read or written the storage medium can bedistinguished. Therefore, if in reading/writing an optical storagemedium, for example, the optical read/write apparatus first reads theidentification information from the extended area, and only when theidentification information readout matches the identificationinformation assigned to the apparatus, is allowed to read or read orwrite the medium, the illegal copying and other uses of the opticalstorage medium can be prevented.

[0352] The optical read/write apparatus may be arranged so that checkingmeans for checking whether the identification information retrieved fromthe extended area of the optical storage medium matches theidentification information of the optical read/write apparatus stored inthe identification information storing means, wherein the controllingmeans controls the illuminating means in reproducing data from theoptical storage medium so as to read identification information storedin the extended area of the optical storage medium, and only when thechecking means determines that the two sets of identificationinformation match, allows data to be read from the recordable area otherthan the extended area of any data storage layer.

[0353] The optical read/write method may be arranged so as to includethe steps of, in reproducing data from the optical storage medium,reading the identification information from the extended area of theoptical storage medium, checking whether the identification informationretrieved from the extended area matches the identification informationof the optical read/write apparatus, and only when the two sets ofidentification information match each other as a result of the checking,starts data to be read from the recordable area other than the extendedarea of any data storage layer.

[0354] According to the arrangement, in reading data from the opticalstorage medium, the optical read/write apparatus first reads theidentification information from the extended area of the optical storagemedium and only when the identification information readout and theidentification information assigned to the apparatus, allows data to beread from the optical storage medium. The illegal copying and other usesof the optical storage medium can be surely prevented.

[0355] An optical read/write apparatus of the present invention causes aread/write light beam from illuminating means to strike only one side ofan optical storage medium and is arranged so as to include: encryptioninformation storing means for storing encryption information by whichdata is encrypted before being recorded on the optical storage medium;and controlling means for controlling the illuminating means so that theoptical storage medium holds the encryption information in the extendedarea.

[0356] An optical read/write method of the present invention is arrangedto include the steps of: preparing the optical storage medium; preparingencryption information by which data is encrypted before being stored inthe optical storage medium; and storing the encryption information inthe extended area.

[0357] According to the arrangement, the extended area of the opticalstorage medium can hold encryption information by which data isencrypted before being stored in the optical storage medium. Therefore,if when the optical read/write apparatus records information on theoptical storage medium, encryption information is read out from theextended area and information is encrypted based on the encryptioninformation before being stored on the optical storage medium, it isonly the optical read/write apparatus which can decrypt the encryptioninformation that can decrypt the information read out from the opticalstorage medium. Therefore, the illegal copying and other uses of theoptical storage medium can be prevented.

[0358] The optical read/write apparatus may be arranged so as to furtherinclude encrypting means for encrypting data recorded on the opticalstorage medium in reference to encryption information in the extendedarea, wherein the controlling means controls the illuminating means sothat recording information encrypted by the encrypting means is storedin the data storage layer.

[0359] The optical read/write method may be arranged so as to furtherinclude the steps of encrypting data to be recorded on the opticalstorage medium in reference to the encryption information in theextended area and recording the encrypted recording information in thedata storage layer.

[0360] According to the arrangement, based on the encryption informationstored in the extended area of the optical storage medium, informationto be recorded on the optical storage medium is encrypted before beingrecorded on the optical storage medium.

[0361] The optical read/write apparatus may be further arranged so thatthe controlling means allows reproduction of only the recordinginformation which is encrypted based on the same encryption informationas the encryption information stored in the encryption informationstoring means.

[0362] The optical read/write method may be further arranged so thatonly the recording information encrypted based on the same encryptioninformation as the encryption information prepared in advance.

[0363] According to the arrangement, only the information can bereproduced which is encrypted using the same encryption information asthe encryption information assigned to the optical read/write apparatus.Thus, the illegal copying and other uses of the optical storage mediumcan be prevented if optical read/write apparatuses other than theoptical read/write apparatus provided with the encryption informationare used.

[0364] An optical read/write apparatus of the present invention causes aread/write light beam from illuminating means to strike only one side ofthe optical storage medium and is arranged so as to include controllingmeans for controlling the illuminating means so as to test write data inthe extended area.

[0365] An optical read/write method of the present invention is arrangedto include the steps of preparing the optical storage medium, and testwriting data in the extended area.

[0366] According to the arrangement, the extended area can be utilizedas a test write area to determine the most suitable light beam intensityin, for example, writing on the optical storage medium. This eliminatesthe need to provide a separate test write area in the recordable areaother than the extended area of the optical storage medium and allowsfor more efficient use of the recordable area of the optical storagemedium.

[0367] The optical storage medium may be arranged so that the extendedarea constitutes a fully prerecorded pseudo-recording area.

[0368] According to the arrangement, the pseudo-recording area providesthe functions of the extended area. Further, the recordable area otherthan the pseudo-recording area of the first data storage layer is aslarge as the recordable area of the second data storage layer, and theposition of the illuminating means relative to the optical storagemedium can be controlled in the same manner with respect to read/writein the recordable area of the first data storage layer and with respectto read/write in the recordable area of the second data storage layer.

[0369] The optical storage medium may be arranged so that thepseudo-recording area stores identification information which is uniqueto an individual optical storage medium and by which the optical storagemedium is distinguished from other optical storage media.

[0370] According to the arrangement, in reading or writing data on theoptical storage medium using an optical read/write apparatus, theoptical storage medium is readable/writeable only with the opticalread/write apparatus which matches the identification information. Thus,the illegal copying and other uses of the optical storage medium can beprevented.

[0371] The optical storage medium may be arranged so that thepseudo-recording area stores encryption information to encryptinformation to be stored on the optical storage medium.

[0372] According to the arrangement, when the optical read/writeapparatus records information on the optical storage medium, the opticalread/write apparatus first reads the encryption information from thepseudo-recording area, encrypts the information based on the encryptioninformation before the information is stored on the optical storagemedium; thus, it is only the optical read/write apparatus that candecrypt the encryption information that can decrypt the information readout from the optical storage medium. Therefore, the illegal copying andother uses of the optical storage medium can be prevented.

[0373] An optical read/write apparatus of the present invention causes aread/write light beam from illuminating means to strike only one side ofthe optical storage medium, and is arranged so as to include: encryptingmeans for encrypt data recorded on the optical storage medium inreference to the encryption information in the pseudo-recording area;and controlling means for controlling the illuminating means so that therecording information encrypted by the encrypting means is recorded inthe data storage layer.

[0374] An optical read/write method of the present invention is arrangedto include the steps of preparing the optical storage medium; encryptingdata recorded on the optical storage medium in reference to theencryption information in the pseudo-recording area; and recording theencrypted recording information in the data storage layer.

[0375] According to the arrangement, information can be encrypted basedon the encryption information recorded in the pseudo-recording area ofthe optical storage medium before being recorded on the optical storagemedium.

[0376] The optical storage medium may be arranged so that thepseudo-recording area is not rewriteable.

[0377] According to the arrangement, the identification information andthe encryption information stored in the optical storage medium

pseudo-recording area can be protected. The illegal copying and otheruses of the optical storage medium is better prevented.

[0378] In addition, as described earlier, in the present invention, inan arrangement whereby: a lumped address scheme is used, multiple datastorage layers are readable/writeable using a light incident to only oneside; and the optical transmittance varies due to the recording usingincident light, attempts are made to achieve desirable read/writecharacteristics.

[0379] To this end, for example, the optical disk 101 includes stackeddata storage layers each of which is readable/writeable separately fromthe other data storage layers and each data storage layer has an addressarea 104 in which address pits 112 are collectively formed. The seconddata storage layer of the optical disk 101 is readable/writeable usinglight transmitted through the first data storage layer. The address area104 of the first data storage layer has a continuous storage area 114where the transmittance has varied and a non-recorded area where thetransmittance has not varied. Thus, the quantity of light transmittedthrough the address area 104 is made closer to the quantity of lighttransmitted through the non-address area 105.

[0380] An optical storage medium of the present invention includesstacked multiple data storage layer each of which is readable/writeableseparately from the other data storage layers by means of only a lightbeam striking one side of the optical storage medium, each of the datastorage layers having address tracks and at least one address area wherethere are collectively formed address information portions representingaddress information, the optical storage medium exhibiting an opticaltransmittance which varies when data is written by means of the incidentlight, and is arranged so that one of every adjacent two of the addresstracks in the address area of a first data storage layer is continuouslyrecorded by means of the incident light, and the other is unrecorded,the first data storage layer being one of the data storage layers whichis located closest to a light-striking surface of the optical storagemedium, a second data storage layer being another of the data storagelayers which is located next to the first data storage layer, oppositethe light-striking surface.

[0381] In addition, an optical read/write apparatus of the presentinvention causes a read/write light beam from illuminating means tostrike only one side of an optical storage medium including multiplestacked data storage layers each of which is readable/writeableseparately from the other data storage layers by means of only a lightbeam striking one side of the optical storage medium, each of the datastorage layers having multiple address tracks and at least one addressarea where there are collectively formed address information portionsrepresenting address information, the optical storage medium exhibitingan optical transmittance which varies when data is written by means ofthe light beam, and is arranged so that the optical read/write apparatusincludes controlling means for controlling the illuminating means sothat one of every adjacent two of the address tracks in the address areaof a first data storage layer is continuously recorded by means of theincident light, and the other one is unrecorded, the first data storagelayer being one of the data storage layers which is located closest to alight-striking surface of the medium, a second data storage layer beinganother of the data storage layers which is located next to the firstdata storage layer; opposite the light-striking surface.

[0382] In addition, an optical read/write method of the presentinvention includes the step of causing a read/write light beam to strikeonly one side of an optical storage medium including multiple stackeddata storage layers each of which is readable/writeable separately fromthe other data storage layers by means of only a light beam striking oneside of the optical storage medium, each of the data storage layershaving multiple address tracks and at least one address area where thereare collectively formed address information portions representingaddress information, the optical storage medium exhibiting an opticaltransmittance which varies when data is written by means of the lightbeam, and is arranged so as to further include the step of continuouslyrecording one of every adjacent two of the address tracks in the addressarea of a first data storage layer by means of the incident light, whileleaving the other one unrecorded, the first data storage layer being oneof the data storage layers which is located closest to a light-strikingsurface of the medium, a second data storage layer being another of thedata storage layers which is located next to the first data storagelayer, opposite the light-striking surface.

[0383] According to the arrangement, one of every adjacent two of theaddress tracks in the address area of the first data storage layerlocated close to the light-striking surface of the optical storagemedium is continuously recorded by means of the incident light, and theother is unrecorded. Therefore, in reading/writing in the second datastorage layer, in a case where the light projected to focus on thesecond data storage layer forms a light spot on the first data storagelayer, the recorded area encompassed in the light spot of a non-addressarea in the recordable area of the first data storage layer, forexample, the sum of the areas of the recording marks, is substantiallyequal to the sum of the continuously recorded areas encompassed in thelight spot in the address area of the first data storage layer.

[0384] Thus, the intensity of light projected on the second data storagelayer after passing through the address area of the first data storagelayer of the optical storage medium can be made substantially equal tothe intensity of light projected on the second data storage layer afterpassing through the non-address area in the recordable area of the firstdata storage layer. As a result, read/write operations on the seconddata storage layer become more stable and desirable.

[0385] In addition, if the address area of the first data storage layerof the optical storage medium is continuously recorded using the opticalread/write apparatus of the present invention or the optical read/writemethod in the aforementioned manner, the cost of the optical disk can bereduced by reducing the manufacturing steps of the optical disk.

[0386] The optical read/write apparatus may be arranged so that thecontrolling means, after reproducing the address information, controlsthe illuminating means based on the obtained address information so thatone of every adjacent two of the address tracks is continuously recordedand the other one is unrecorded.

[0387] The optical read/write method may be arranged so that afterreproducing the address information, one of every adjacent two of theaddress tracks is continuously recorded and the other one is unrecorded,based on the obtained address information.

[0388] According to the arrangement, one of every adjacent two of theaddress tracks is continuously recorded and the other one is unrecorded,based on the address information derived from the address area.Therefore, the optical storage medium does not require a particulararrangement to determine whether the address track is to be continuouslyrecorded or unrecorded.

[0389] An optical storage medium of the present invention includesmultiple stacked data storage layers each of which is readable/writeableseparately from the other data storage layers by means of only a lightbeam striking one side of the optical storage medium, each of the datastorage layers having address tracks and at least one address area wherethere are collectively formed address information portions representingaddress information, the optical storage medium exhibiting an opticaltransmittance which varies when data is written by means of the lightbeam, and is arranged so that each of the address tracks in the addressarea of a first data storage layer has a judgement mark to show whetherthe address track is to be continuously recorded or left unrecorded, thefirst data storage layer being one of the data storage layers which islocated closest to a light-striking surface of the medium, a second datastorage layer being another of the data storage layers which is locatednext to the first data storage layer, opposite the light-strikingsurface.

[0390] In addition, an optical read/write apparatus of the presentinvention causes a read/write light beam from illuminating means tostrike only one side of the optical storage medium, and is arranged soas to include controlling means for determining based on informationreproduced from the judgement mark whether each of the address tracks inthe address area is to be continuously recorded or left unrecorded andcontrolling the illuminating means according to a result of thedetermination so that each of the address tracks is to be eithercontinuously recorded or left unrecorded.

[0391] In addition, an optical read/write method of the presentinvention includes the step of causing a read/write light beam to strikeonly one side of the optical storage medium, and is arranged so as tofurther include the steps of determining based on information reproducedfrom the judgement mark whether each of the address tracks in theaddress area is to be continuously recorded or left unrecorded andcontrolling according to a result of the determination so that each ofthe address tracks is to be continuously recorded by means of theincident light or left unrecorded.

[0392] According to the arrangement, each of the address tracks in theaddress area of the first data storage layer located on thelight-striking side of the optical storage medium has a judgement markshowing whether the address track should be continuously recorded orleft unrecorded. The optical read/write apparatus in which the opticalstorage medium is loaded can readily form based on the judgement mark acontinuously recorded area in an address area of the first data storagelayer of the optical storage medium.

[0393] In addition, the optical read/write apparatus can immediatelydetermine based on the judgement mark whether to continuously record theaddress track and therefore quickly complete the process to continuouslyrecord the address track in the address area.

[0394] In addition, the judgement mark is specified to change into thefollowing state, provided that an area in a non-address area iscontinuously recorded based on an instruction from the judgement mark.That is, the judgement mark is specified so that in reading/writing inthe second data storage layer, in a case where the light projected tofocus on the second data storage layer forms a light spot on the firstdata storage layer, the recorded area encompassed in the light spot of anon-address area in the recordable area of the first data storage layer,for example, the sum of the areas of the recording marks, issubstantially equal to the sum of the continuously recorded areasencompassed in the light spot in the address area of the first datastorage layer. To this end, the judgement mark shows that, for example,one of every adjacent two of the address tracks in, for example, thefirst data storage layer is continuously recorded and the other one isleft unrecorded. As a result, using the optical storage medium of thepresent invention, read/write operations on the second data storagelayer become more stable and desirable.

[0395] In addition, according to the optical read/write apparatus of thepresent invention or the optical read/write method, the process ofcontinuously recording the address area of the first data storage layerof the optical storage medium can be implemented after the shipment ofthe optical storage medium in the aforementioned manner, and the cost ofthe optical storage medium can be reduced by reducing the manufacturingsteps of the optical storage medium.

[0396] An optical storage medium of the present invention includesmultiple stacked data storage layers each of which is readable/writeableon both a land and a groove formed on the data storage layer separatelyfrom the other data storage layers by means of only a light beamstriking one side of the optical storage medium, each of the datastorage layers having multiple address tracks and at least one addressarea where there are collectively formed address information portionsrepresenting address information, the optical storage medium exhibitingan optical transmittance which varies when data is written by means ofthe light beam, and is arranged so that: among the address tracks in theaddress area of a first data storage layer, either those address trackswhich extend from the land or those address tracks which extend from thegroove are continuously recorded by means of the incident light, and theothers are unrecorded, the first data storage layer being one of thedata storage layers which is located closest to a light-striking surfaceof the medium, a second data storage layer being another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface.

[0397] In addition, an optical read/write apparatus of the presentinvention causing a read/write light beam from illuminating means tostrike only one side of an optical storage medium including multiplestacked data storage layers each of which is readable/writeable on botha land and a groove formed on the data storage layer separately from theother data storage layer by means of a light beam striking one side ofthe optical storage medium, each of the data storage layers havingmultiple address tracks and at least one address area where there arecollectively formed address information portions representing addressinformation, the optical storage medium exhibiting an opticaltransmittance which varies when data is written by means of the lightbeam, and is arranged to include controlling means for controlling theilluminating means so that in the address area of a first data storagelayer, either those address tracks which extend from the land or thosewhich extend from the groove are continuously recorded by means of theincident light, and the others are unrecorded, the first data storagelayer being one of the data storage layers which is located closest to alight-striking surface of the medium, a second data storage layer beinganother of the data storage layers which is located next to the firstdata storage layer, opposite the light-striking surface.

[0398] In addition, an optical read/write method of the presentinvention includes the step of causing a read/write light beam to strikeonly one side of an optical storage medium including multiple stackeddata storage layers each of which is readable/writeable on both a landand a groove formed on the data storage layer separately from the otherdata storage layers by means of only a light beam striking one side ofthe optical storage medium, each of the data storage layers havingmultiple address tracks and at least one address area where there arecollectively formed address information portions representing addressinformation, the optical storage medium exhibiting an opticaltransmittance which varies when data is written by means of the lightbeam, and is arranged so that in the address area of a first datastorage layer, either those address tracks which extend from the land orthose which extend from the groove are continuously recorded

by means of the incident light, and there others are unrecorded, thefirst data storage layer being one of the data storage layers which islocated closest to a light-striking surface of the medium, a second datastorage layer being another of the data storage layers which is locatednext to the first data storage layer, opposite the light-strikingsurface.

[0399] According to the arrangement, in the address area of the firstdata storage layer on the light-striking side, either those addresstracks which extend from the land or those which extend from the grooveare continuously recorded when data is written by means of incidentlight, and the others are left unrecorded. Therefore, in reading/writingon the second data storage layer, in a case where the light projected tofocus on the second data storage layer forms a light spot on the firstdata storage layer, the recorded area encompassed in the light spot of anon-address area in the recordable area of the first data storage layer,for example, the sum of the areas of the recording marks, issubstantially equal to the sum of the continuously recorded areasencompassed in the light spot in the address area of the first datastorage layer.

[0400] Thus, the intensity of light transmitted through the address areaof the first data storage layer before reaching the second data storagelayer can be made substantially equal to the intensity of lighttransmitted through the non-address area in the recordable area of thefirst data storage layer before reaching the second data storage layer.As a result, read/write operations on the second data storage layerbecome more stable and desirable.

[0401] An optical storage medium of the present invention includesmultiple stacked data storage layers each of which is readable/writeableon both a land and a groove formed on the data storage layer separatelyfrom the other data storage layers by means of only a light beamstriking one side of the optical storage medium, each of the datastorage layers having multiple address tracks and at least one addressarea where there are collectively formed address information portionsrepresenting address information, the optical storage medium exhibitingan optical transmittance when data is written by means of the lightbeam, and is arranged so that: in a first data storage layer, theaddress area has a first address area and a second address area whichare adjacent to each other along tracks, the first data storage layerbeing one of the data storage layers which is located closest to alight-striking surface of the medium a second data storage layer beinganother of the data storage layers which is located next to the firstdata storage layer, opposite the light-striking surface; the addressinformation portions in either the first and second address areas areformed in those address tracks which extend from the land, and theaddress information portions in the other one of the first and secondaddress areas are formed in those address tracks which extend from thegroove; and either an area where the address information portions areformed or an area where no address information portions are formed iscontinuously recorded.

[0402] In addition, an optical read/write apparatus of the presentinvention causes a read/write light beam from illuminating means tostrike only one side of an optical storage medium including multiplestacked data storage layers each of which is readable/writeable on botha land and a groove formed on the data storage layer separately from theother data storage layers by means of only a light beam striking oneside of the optical storage medium, each of the data storage layershaving multiple address tracks and at least one address area where thereare collectively formed address information portions representingaddress information, the optical storage medium exhibiting an opticaltransmittance which varies when data is written by means of the lightbeam, and is arranged so as to include controlling means for controllingthe illuminating means so that: in a first data storage layer, theaddress area has a first address area and a second address area whichare adjacent to each other along tracks, the first data storage layerbeing one of the data storage layers which is located closest to alight-striking surface of the medium, a second data storage layer beinganother of the data storage layers which is located next to the firstdata storage layer, opposite the light-striking surface; and when theaddress information portions in either one of the first and secondaddress areas are formed in those address tracks which extend from theland, and the address information portions in the other one of the firstand second address areas are formed in those address tracks which extendfrom the groove, either an area where the address information portionsare formed or an area where no address information portions are formedis continuously recorded in the first and second address areas.

[0403] In addition, an optical read/write method of the presentinvention comprises the step of causing a read/write light beam tostrike only one side of an optical storage medium including multiplestacked data storage layers each of which is readable/writeable on botha land and a groove formed on the data storage layer by means of only alight beam striking one side of the optical storage medium, each of datastorage layers having multiple address tracks and at least one addressarea where there are collectively formed address information portionsrepresenting address information, the optical storage medium exhibitingan optical transmittance which varies when data is written by means ofthe light beam, and is arranged so that: in a first data storage layer,the address area has a first address area and a second address areawhich are adjacent to each other along tracks, the first data storagelayer being one of the data storage layers which is located closest to alight-striking surface of the medium, a second data storage layer beinganother of the data storage layers which is located next to the firstdata storage layer, opposite the light-striking surface; and the methodfurther comprises the steps of, when the address information portions ineither one of the first and second address areas are formed in thoseaddress tracks which extend from the land, and the address informationportions in the other one of the first and second address areas areformed in those address tracks which extend from the groove,continuously recording either an area where the address informationportions are formed or an area where no address information portions areformed in the first and second address areas by means of the incidentlight.

[0404] According to the arrangement, the address area of the first datastorage layer located on the light-striking side of the optical storagemedium is made of a first address area and a second address area whichare adjacent to each other along tracks; the address informationportions in either one of the first and second address areas are formedin those address tracks which extend from the land, and the addressinformation portions in the other one of the first and second addressareas are formed in those address tracks which extend from the groove;and either an area where the address information portions are formed oran area where no address information portions are formed is continuouslyrecorded. Therefore, in reading/writing on the second data storagelayer, in a case where the light projected to focus on the second datastorage layer forms a light spot on the first data storage layer, therecorded area encompassed in the light spot of a non-address area in therecordable area of the first data storage layer, for example, the sum ofthe areas of the recording marks, is substantially equal to the sum ofthe continuously recorded areas encompassed in the light spot in theaddress area of the first data storage layer.

[0405] Thus, the intensity of light transmitted through the address areaof the first data storage layer before reaching the second data storagelayer can be made substantially equal to the intensity of lighttransmitted through the non-address area in the recordable area of thefirst data storage layer before reaching the second data storage layer.As a result, read/write operations on the second data storage layerbecome more stable and desirable.

[0406] In addition, if the address area of the first data storage layerof the optical storage medium is continuously recorded using the opticalread/write apparatus of the present invention or the optical read/writemethod in the aforementioned manner, the cost of the optical storagemedium can be reduced by reducing the manufacturing steps of the opticalstorage medium.

[0407] In addition, the present invention enables stable read/write ofinformation on an optical disk with two or more storage layers withoutbeing affected by prepit areas.

[0408] To this end, the optical disk 201 includes a first storage layer215 and a second storage layer 213, an outer prepit area 206 b as aprepit area is provided outside the outer periphery the recordable area203 b of the second storage layer 213. Predetermined information isstored in the outer prepit area 206 b in advance using pits. Prepitinformation is reproduced by transmitting a light beam 217 through arecordable area 203 b of the first storage layer 215 where the opticaltransmittance is high due to recording to the full capacity and thenfocusing on the outer prepit area 206 b. The provision of the outerprepit area 206 b on the second storage layer 213 enables data to beread from and write into the second storage layer 213 without beingaffected by prepit areas.

[0409] An optical storage medium of the present invention is preferablysuch that each of the data storage layers except for the last datastorage layer has a pseudo-recording area at such a position that allowslight to be transmitted to the prepit area, the pseudo-recording area,when fully prerecorded, exhibiting a higher optical transmittance thanother areas.

[0410] In this manner, a pseudo-recording area, when fully prerecorded,exhibiting a higher optical transmittance than other areas is providedat such a position that allows light to be transmitted to the prepitarea, the pseudo-recording area; therefore, the light striking thelight-striking side storage layer can reach the prepit area afterpassing through the pseudo-recording area of any data storage layer, butthe last data storage layer. Therefore, the intensity of thereproduction signal of the prepit information reproduced from prepitarea does not fall. Therefore, the amplitude of the reproduction signalof the prepit information can be made greater.

[0411] Another optical read/write apparatus of the present inventioncauses a read/write light beam from illuminating means to strike onlyone side of the optical storage medium, and is arranged so as toinclude: low frequency variation removing means for removing lowfrequency variations from the reproduction signal obtained from theprepit area; and digital converting means for converting thereproduction signal from which the low frequency variations are removedto a digital signal using the constant voltage as a reference.

[0412] In addition, an optical read/write method of the presentinvention includes the step of causing a read/write light beam fromilluminating means to strike only one side of the optical storagemedium, and is arranged so as to further include the steps of removinglow frequency variations from the reproduction signal obtained from theprepit area; and converting the reproduction signal from which the lowfrequency variations are removed to a digital signal using a constantvoltage as a reference.

[0413] According to the apparatus and method, the reproduction signalobtained from reading off the prepit area is rid of low frequencyvariations by low frequency variation removing means. The reproductionsignal, from which low frequency variations are removed, has an envelopewhose mean level is substantially constant. Thereafter, the reproductionsignal is converted to a digital signal by digital converting meansusing the constant voltage as a reference. In this manner, the envelopecomes to have a substantially constant mean level, in converting areproduction signal to a digital signal, the constant voltage can beused as a reference. Therefore, the digital conversion can be carriedout without being affected by variations in amplitude of thereproduction signal. For example, as mentioned in the foregoing,incident light illuminating a recorded part and a non-recorded part ofthe first storage layer is focused on the second storage layer, adigital signal can be produced stably from the reproduction signal evenif the intensity of the reproduction signal of the prepit informationvaries with the rotation of the optical storage medium. Therefore, theprepit information of the second storage layer of the optical storagemedium can be stably reproduced.

[0414] An optical read/write apparatus of the present invention causes aread/write light beam from illuminating means to strike only one side ofthe storage medium having the pseudo-recording area, and is arranged soas to include: recording status checking means for checking whether thepseudo-recording area is fully recorded or not based on a reproductionsignal obtained from the pseudo-recording area; and pseudo-recordingmeans for fully recording data in the pseudo-recording area if thepseudo-recording area is not fully recorded.

[0415] In addition, an optical read/write method of the presentinvention includes the step of causing a read/write light beam fromilluminating means to strike only one side of the storage medium withthe pseudo-recording area, and is arranged so as to further include thesteps of fully recording the pseudo-recording area so that thepseudo-recording area transmits light therethrough to the prepit area.

[0416] According to the apparatus and method, the recording statuschecking means checks whether or not the pseudo-recording area is fullyrecorded. If the check turns out that the pseudo-recording area is notfully recorded, the pseudo-recording means fully recorded thepseudo-recording area. Thus, the pseudo-recording area of the opticalstorage medium is formed by the optical read/write apparatus, and thereis no need to form a pseudo-recording area on the optical storage mediumin advance before shipment. Therefore, the cost of the optical storagemedium can be reduced.

[0417] Another optical storage medium of the present invention includes:one light-striking side storage layer provided as a data storage layeron a light-striking side; and one or more opposite-side storage layersprovided as data storage layers opposite the light-striking side fromthe light-striking side storage layer, and is arranged so that: thelight-striking side storage layer has a prepit area which includespreformed pits representative of data: and an optically transparentrecordable area of the light-striking side storage layer is formed widerthan the optically transparent recordable areas of the opposite-sidestorage layers.

[0418] With the arrangement, the recordable areas of the opposite-sidestorage layers are smaller than the recordable area on thelight-striking side. Therefore, in a case where the prepit area isprovided adjacent to the recordable area on the light-striking sidestorage layer, light transmitted through the prepit area does not enterthe recordable areas of the opposite-side storage layers. In addition,since light transmitted near the border between the recordable area ofthe light-striking side storage layer and the prepit area is focused onthe recordable areas of the opposite-side storage layers, even if therecordable areas of the opposite-side storage layers are small asmentioned in the foregoing, the light can be transmitted only throughthe recordable area of the light-striking side storage layer and focusedon the recordable areas of the opposite-side storage layers. Therefore,data can be stably read from and written into the last data storagelayer without being affected by the prepit area.

[0419] Another optical storage medium of the present invention includes:one light-striking side storage layer provided as a data storage layeron a light-striking side; and one or more opposite-side storage layersprovided as data storage layers opposite the light-striking side fromthe light-striking side storage layer, and is arranged so that: thelight-striking side storage layer has a prepit area which includespreformed pits representative of data; and the prepit area allowstransmission of light so that light reaches the opposite-side storagelayers, at a transmittance substantially equal to that of a recordablearea of the light-striking side storage layer.

[0420] With the arrangement, since the prepit area allows light to betransmitted at a transmittance substantially equal that as thetransmittance of the recordable area of the light-striking side storagelayer, the light passing through the recordable area and through theprepit area has substantially the same intensity. Therefore, data can beread from and written to the last data storage layer stably withoutbeing affected by the prepit area.

[0421] The storage medium in which the prepit area is provided in thelight-striking side storage layer is preferably such that the recordableareas of the data storage layers except for the last data storage layerwhich is most distanced from the light-striking side storage layerexhibit, when fully recorded, higher optical transmittances than otherareas.

[0422] With the arrangement, in projecting read/write light to therecordable areas of the data storage layers except for the last datastorage layer, the recordable areas come to have higher opticaltransmittances than other areas upon completion of recording. Therefore,keeping the recordable area fully recorded enables the light passingthrough the recordable areas to remain sufficiently intense until itreaches a target data storage layer. Therefore, data can be stably readand written on an optical storage medium with multiple storage layers.

[0423] An optical read/write apparatus causing a read/write light beamfrom illuminating means to strike only one side of the optical storagemedium includes controlling means for controlling the illuminating meansso that the recordable area of the light-striking side storage layer isfully recorded before the recordable areas of the opposite-side storagelayers which are adjacent to the light-striking side storage layer isread/written.

[0424] In addition, an optical read/write method including the step ofcausing a read/write light beam from illuminating means to strike onlyone side of the optical storage medium includes the steps of fullyrecording the recordable area of the light-striking side storage layerand subsequently reading or writing in the recordable areas of theopposite-side storage layers which are adjacent to the light-strikingside storage layer.

[0425] In reading or writing on the optical storage medium using such anapparatus or method, the controlling means controls the illuminatingmeans so that the recordable area of the light-striking side storagelayer fully recorded before the recordable area of a targetopposite-side storage layer is read or written. Therefore, in reading orwriting the opposite-side storage layers, the light passing through thelight-striking side storage layer remains sufficiently intense until itreaches the opposite-side storage layers. Therefore, data can be stablyread and written on the optical storage medium.

[0426] An optical storage medium having the transparent prepit area ispreferably such that the prepit area, under such illumination to fullyrecord the prepit area substantially identically to the recordable area,exhibits a high optical transmittance substantially equal to that of therecordable area.

[0427] With such an arrangement, the prepit area, when fully recordedunder illumination, comes to exhibit a similar optical transmittance tothat of the recordable area. Therefore, the light passing through therecordable area and through the prepit area has substantially the sameintensity. Therefore, data can be read from and written to the last datastorage layer stably.

[0428] With this optical storage medium, preferably, on a pit row of thepits in the prepit area, there is formed a continuous, fully recordedstorage area with neither the pits nor intervening portions between thepits left unrecorded, so that a fully recorded portion occupies asubstantially equal area in a part where light is concentrated in therecordable area and in a part where light is concentrated in the prepitarea.

[0429] With the arrangement, light forms a beam spot in both therecordable area and the prepit area as it strikes the recordable areaand the prepit area of the light-striking side storage layer. Thecontinuous storage area is formed on the pit row so that the area of therecorded portion in a part where light is concentrated in the beam spotis substantially equal between the recordable area and the prepit area.Therefore, light transmitted through the recordable area and the prepitarea has similar intensity. Therefore, data can be stably read from orwritten into the last data storage layer.

[0430] An optical read/write apparatus causing a read/write light beamfrom illuminating means to strike only one side of the optical storagemedium of which the prepit area exhibits a high optical transmittanceunder illumination includes: continuous storage area checking means forchecking based on a signal reproduced from the prepit area whether ornot the prepit area has a continuous storage area where areas interposedbetween the pits are continuously and fully recorded as to a pit row ofthe pits; and continuous recording means for performing such recordingthat on the pit row in the prepit area where the continuous storage areais not present, there is formed the continuous storage area so that afully recorded portion occupies a substantially equal area in a partwhere light is concentrated in the recordable area and in a part wherelight is concentrated in the prepit area.

[0431] In addition, an optical read/write method including the step ofcausing a read/write light beam from illuminating means to strike onlyone side of the optical storage medium further includes the step ofperforming such recording that on the pit row in the prepit area wherethe continuous storage area is not present, there is formed thecontinuous storage area where areas interposed between the pits arecontinuously and fully recorded as to a pit row of the pits so that afully recorded portion occupies a substantially equal area in a partwhere light is concentrated in the recordable area and in a part wherelight is concentrated in the prepit area.

[0432] With the apparatus and method, the continuous storage areachecking means checks whether there is a continuous storage area. If thecheck turns out that there is a continuous storage area, the continuousrecording means performs recording to form a continuous storage area.Thus, the formation of a continuous storage area on the optical storagemedium using the optical read/write apparatus eliminates the need toform a continuous storage area on the optical storage medium in advancebefore shipment. Therefore, the cost of the optical storage medium canbe reduced.

[0433] The invention being thus described, it will be obvious that thesame way may be varied in many ways. Such variations are not to beregarded as a departure from the spirit and scope of the invention, andall such modifications as would be obvious to one skilled in the art areintended to be included within the scope of the following claims.

What is claimed is:
 1. An optical storage medium, comprising stackeddata storage layers each of which is readable/writeable separately fromthe other layers by means of only a light beam striking one side of theoptical storage medium, wherein a recordable area of a first datastorage layer has adjacent to an end thereof an extended area coveringmore than an area directly above a recordable area of a second datastorage layer in a direction in which the first and second data storagelayers are stacked, the first data storage layer being one of the datastorage layers which is located closest to a light-striking surface ofthe medium, the second data storage layer being another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface.
 2. The optical read/write apparatusas set forth in claim 1, wherein the extended area is a pseudo-recordingarea which is fully prerecorded.
 3. The optical read/write apparatus asset forth in claim 2, wherein the pseudo-recording area storesidentification information which is unique to the optical storage mediumand by which the optical storage medium is distinguished from otheroptical storage media.
 4. The optical read/write apparatus as set forthin claim 3, wherein information in the pseudo-recording area is notrewriteable.
 5. The optical read/write apparatus as set forth in claim2, wherein the pseudo-recording area stores encryption information bywhich data is encrypted before being recorded on the optical storagemedium.
 6. The optical read/write apparatus as set forth in claim 5,wherein information in the pseudo-recording area is not rewriteable. 7.The optical read/write apparatus as set forth in claim 1, wherein thedata storage layers exhibit a lower optical reflectance in recordedareas than in non-recorded areas.
 8. An optical read/write apparatuscausing a read/write light beam from illuminating means to strike onlyone side of an optical storage medium including stacked data storagelayers each of which is readable/writeable separately from the otherlayers by means of only a light beam striking one side of the medium,wherein: the medium is such that a recordable area of a first datastorage layer has adjacent to an end thereof an extended area coveringmore than an area directly above a recordable area of a second datastorage layer in a direction in which the first and second data storagelayers are stacked, the first data storage layer being one of the datastorage layers which is located closest to a light-striking surface ofthe medium, the second data storage layer being another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface; and the apparatus comprisingcontrolling means for controlling the illuminating means so that theextended area of the optical storage medium is fully recorded before arecordable area of the first data storage layer of the optical storagemedium is recorded except for the extended area.
 9. The opticalread/write apparatus as set forth in claim 8, wherein the opticalstorage medium exhibits a lower optical reflectance in recorded areas ofthe data storage layers than in non-recorded areas thereof.
 10. Anoptical read/write apparatus causing a read/write light beam fromilluminating means to strike only one side of an optical storage mediumincluding stacked data storage layers each of which isreadable/writeable separately from the other layers by means of only alight beam striking one side of the medium, wherein: the medium is suchthat: a recordable area of a first data storage layer has adjacent to anend thereof an extended area covering more than an area directly above arecordable area of a second data storage layer in a direction in whichthe first and second data storage layers are stacked, the first datastorage layer being one of the data storage layers which is locatedclosest to a light-striking surface of the medium, the second datastorage layer being another of the data storage layers which is locatednext to the first data storage layer, opposite the light-strikingsurface; the extended area is a pseudo-recording area which is fullyprerecorded; and the pseudo-recording area stores encryption informationby which data is encrypted before being recorded on the optical storagemedium, and the apparatus comprising: encrypting means for encryptingdata to be recorded on the optical storage medium using the encryptioninformation stored in the pseudo-recording area; and controlling meansfor controlling the illuminating means so that data is encrypted by theencrypting means before being recorded in any of the data storagelayers.
 11. The optical read/write apparatus as set forth in claim 10,wherein the optical storage medium exhibits a lower optical reflectancein recorded areas of the data storage layers than in non-recorded areasthereof.
 12. An optical read/write apparatus causing a read/write lightbeam from illuminating means to strike only one side of an opticalstorage medium including stacked data storage layers each of which isreadable/writeable separately from the other layers by means of only alight beam striking one side of the medium, wherein: the medium is suchthat a recordable area of a first data storage layer has adjacent to anend thereof an extended area covering more than an area directly above arecordable area of a second data storage layer in a direction in whichthe first and second data storage layers are stacked, the first datastorage layer being one of the data storage layers which is locatedclosest to a light-striking surface of the medium, the second datastorage layer being another of the data storage layers which is locatednext to the first data storage layer, opposite the light-strikingsurface; and the apparatus comprising: identification informationstoring means for storing identification information which is unique tothe optical read/write apparatus and by which the optical read/writeapparatus is distinguished from other optical read/write apparatuses;and controlling means for controlling the illuminating means so that theoptical storage medium holds the identification information in theextended area.
 13. The optical read/write apparatus as set forth inclaim 12, further comprising checking means for checking whether theidentification information retrieved from the extended area of theoptical storage medium matches the identification information of theoptical read/write apparatus stored in the identification informationstoring means, wherein the controlling means controls the illuminatingmeans in reproducing data from the optical storage medium so as to readidentification information stored in the extended area of the opticalstorage medium, and only when the checking means determines as a resultof the check that the two sets of identification information match,allows data to be read from the recordable area other than the extendedarea of any of the data storage layers
 14. The optical read/writeapparatus as set forth in claim 12, wherein the optical storage mediumexhibits a lower optical reflectance in recorded areas of the datastorage layers than in non-recorded areas thereof.
 15. An opticalread/write apparatus causing a read/write light beam from illuminatingmeans to strike only one side of an optical storage medium includingstacked data storage layers each of which is readable/writeableseparately from the other layers by means of only a light beam strikingone side of the medium, wherein: the medium is such that a recordablearea of a first data storage layer has adjacent to an end thereof anextended area covering more than an area directly above a recordablearea of a second data storage layer in a direction in which the firstand second data storage layers are stacked, the first data storage layerbeing one of the data storage layers which is located closest to alight-striking surface of the medium, the second data storage layerbeing another of the data storage layers which is located next to thefirst data storage layer, opposite the light-striking surface, theapparatus comprising: encryption information storing means for storingencryption information by which data is encrypted before being recordedon the optical storage medium; and controlling means for controlling theilluminating means so that the optical storage medium holds theencryption information in the extended area.
 16. The optical read/writeapparatus as set forth in claim 15, further comprising encrypting meansfor encrypting data to be recorded on the optical storage medium usingthe encryption information stored in the extended area, wherein thecontrolling means controls the illuminating means so that data isencrypted by the encrypting means before being recorded in any of thedata storage layers.
 17. The optical read/write apparatus as set forthin claim 16, wherein the controlling means controls so as to allowreproduction of only recorded data which is encrypted using encryptioninformation which is identical to the encryption information stored inthe encryption information storing means.
 18. An optical read/writeapparatus causing a read/write light beam from illuminating means tostrike only one side of an optical storage medium including stacked datastorage layers each of which is readable/writeable separately from theother layers by means of only a light beam striking one side of themedium, wherein: the optical storage medium is such that a recordablearea of a first data storage layer has adjacent to an end thereof anextended area covering more than an area directly above a recordablearea of a second data storage layer in a direction in which the firstand second data storage layers are stacked, the first data storage layerbeing one of the data storage layers which is located closest to alight-striking surface of the medium, the second data storage layerbeing another of the data storage layers which is located next to thefirst data storage layer, opposite the light-striking surface; and theapparatus comprises controlling means for controlling the illuminatingmeans so as to test write data in the extended area.
 19. The opticalread/write apparatus as set forth in claim 18, wherein the opticalstorage medium exhibits a lower optical reflectance in recorded areas ofthe data storage layers than in non-recorded areas thereof.
 20. Anoptical read/write method using an optical storage medium includingstacked data storage layers each of which is readable/writeableseparately from the other layers by means of only a light beam strikingone side of the optical storage medium, wherein: the optical storagemedium is such that a recordable area of a first data storage layer hasadjacent to an end thereof an extended area covering more than an areadirectly above a recordable area of a second data storage layer in adirection in which the first and second data storage layers are stacked,the first data storage layer being one of the data storage layers whichis located closest to a light-striking surface of the medium, the seconddata storage layer being another of the data storage layers which islocated next to the first data storage layer, opposite thelight-striking surface; and the method comprises the step of fullyrecording the extended area before recording a recordable area of thefirst data storage layer of the optical storage medium except for theextended area.
 21. An optical read/write method using an optical storagemedium including stacked data storage layers each of which isreadable/writeable separately from the other layers by means of only alight beam striking one side of the optical storage medium, wherein: theoptical storage medium is such that: a recordable area of a first datastorage layer has adjacent to an end thereof an extended area coveringmore than an area directly above a recordable area of a second datastorage layer in a direction in which the first and second data storagelayers are stacked, the first data storage layer being one of the datastorage layers which is located closest to a light-striking surface ofthe medium, the second data storage layer being another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface; the extended area is apseudo-recording area which is fully prerecorded; and thepseudo-recording area stores encryption information by which data isencrypted before being recorded on the optical storage medium; and themethod comprises the step of encrypting data using the encryptioninformation stored in the pseudo-recording area before recording thedata in any of the data storage layers of the optical storage medium.22. An optical read/write method using an optical storage mediumincluding stacked data storage layers each of which isreadable/writeable separately from the other layers by means of only alight beam striking one side of the optical storage medium, wherein: theoptical storage medium is such that a recordable area of a first datastorage layer has adjacent to an end thereof an extended area coveringmore than an area directly above a recordable area of a second datastorage layer in a direction in which the first and second data storagelayers are stacked, the first data storage layer being one of the datastorage layers which is located closest to a light-striking surface ofthe medium, the second data storage layer being another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface; and the method comprises the stepof storing in the extended area identification information which isunique to an optical read/write apparatus performing read/writefrom/into the optical storage medium and by which the optical read/writeapparatus is distinguished from other optical read/write apparatuses.23. The optical read/write method as set forth in claim 22, comprisingthe steps of: reading the identification information from the extendedarea of the optical storage medium in reproducing data from the opticalstorage medium; checking whether or not the identification informationread from the extended area matches the identification information ofthe optical read/write apparatus; and only when the two sets ofidentification information match, allowing data to be read from therecordable area other than the extended area of any of the data storagelayers.
 24. An optical read/write method using an optical storage mediumincluding stacked data storage layers each of which isreadable/writeable separately from the other layers by means of only alight beam striking one side of the optical storage medium, wherein: theoptical storage medium is such that a recordable area of a first datastorage layer has adjacent to an end thereof an extended area coveringmore than an area directly above a recordable area of a second datastorage layer in a direction in which the first and second data storagelayers are stacked, the first data storage layer being one of the datastorage layers which is located closest to a light-striking surface ofthe medium, the second data storage layer being another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface; and the method comprises the stepsof: preparing encryption information by which data is encrypted beforebeing recorded on the optical storage medium; and recording theencryption information in the extended area.
 25. The optical read/writemethod as set forth in claim 24, further comprising the steps of:encrypting data to be recorded on the optical storage medium usingencryption information read from the extended area; and recording theencrypted data in the data storage layer.
 26. The optical read/writemethod as set forth in claim 25, further comprising the step of allowingreproduction of only recorded data which is encrypted using encryptioninformation which is identical to the prepared encryption information.27. An optical read/write method using an optical storage mediumincluding stacked data storage layers each of which isreadable/writeable separately from the other layers by means of only alight beam striking one side of the optical storage medium, wherein: theoptical storage medium is such that a recordable area of a first datastorage layer has adjacent to an end thereof an extended area coveringmore than an area directly above a recordable area of a second datastorage layer in a direction in which the first and second data storagelayers are stacked, the first data storage layer being one of the datastorage layers which is located closest to a light-striking surface ofthe medium, the second data storage layer being another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface; the method comprises the step oftest writing data in the extended area.
 28. An optical storage medium,comprising stacked data storage layers each of which isreadable/writeable separately from the other layers by means of only alight beam striking one side of the optical storage medium, each of thedata storage layers having at least one address area where there arecollectively formed address information portions representing addressinformation, the optical storage medium exhibiting an opticaltransmittance which varies when data is written by means of the lightbeam, wherein the address area of a first data storage layer includes arecorded area exhibiting a varied transmittance and a non-recorded areaexhibiting an original transmittance, the first data storage layer beingone of the data storage layers which is located closest to alight-striking surface of the medium, a second data storage layer beinganother of the data storage layers which is located next to the firstdata storage layer, opposite the light-striking surface.
 29. The opticalstorage medium as set forth in claim 28, wherein the data storage layersexhibit a lower optical reflectance in recorded areas than innon-recorded areas.
 30. An optical storage medium, comprising stackeddata storage layers each of which is readable/writeable separately fromthe other layers by means of only a light beam striking one side of theoptical storage medium, each of the data storage layers having addresstracks and at least one address area where there are collectively formedaddress information portions representing address information, theoptical storage medium exhibiting an optical transmittance which varieswhen data is written by means of the light beam, wherein one of everyadjacent two of the address tracks in the address area of a first datastorage layer is continuously recorded by means of the incident light,and the other one is unrecorded, the first data storage layer being oneof the data storage layers which is located closest to a light-strikingsurface of the medium, a second data storage layer being another of thedata storage layers which is located next to the first data storagelayer, opposite the light-striking surface.
 31. The optical storagemedium as set forth in claim 30, wherein the data storage layers exhibita lower optical reflectance in recorded areas than in non-recordedareas.
 32. An optical storage medium, comprising stacked data storagelayers each of which is readable/writeable separately from the otherlayers by means of only a light beam striking one side of the opticalstorage medium, each of the data storage layers having address tracksand at least one address area where there are collectively formedaddress information portions representing address information, theoptical storage medium exhibiting an optical transmittance which varieswhen data is written by means of the light beam, wherein each of theaddress tracks in the address area of a first data storage layer has ajudgement mark to show whether the address track is to be continuouslyrecorded or left unrecorded, the first data storage layer being one ofthe data storage layers which is located closest to a light-strikingsurface of the medium, a second data storage layer being another of thedata storage layers which is located next to the first data storagelayer, opposite the light-striking surface.
 33. The optical storagemedium as set forth in claim 32, wherein the data storage layers exhibita lower optical reflectance in recorded areas than in non-recordedareas.
 34. An optical storage medium, comprising stacked data storagelayers each of which is readable/writeable on both a land and a grooveformed on the data storage layer separately from the other layers bymeans of only a light beam striking one side of the optical storagemedium, each of the data storage layers having address tracks and atleast one address area where there are collectively formed addressinformation portions representing address information, the opticalstorage medium exhibiting an optical transmittance which varies whendata is written by means of the light beam, wherein in the address areaof a first data storage layer, either those address tracks which extendfrom the land or those which extend from the groove are continuouslyrecorded by means of the incident light, and the others are unrecorded,the first data storage layer being one of the data storage layers whichis located closest to a light-striking surface of the medium, a seconddata storage layer being another of the data storage layers which islocated next to the first data storage layer, opposite thelight-striking surface.
 35. The optical storage medium as set forth inclaim 34, wherein the data storage layers exhibit a lower opticalreflectance in recorded areas than in non-recorded areas.
 36. An opticalstorage medium, comprising stacked data storage layers each of which isreadable/writeable on both a land and a groove formed on the datastorage layer separately from the other layers by means of only a lightbeam striking one side of the optical storage medium, each of the datastorage layers having address tracks and at least one address area wherethere are collectively formed address information portions representingaddress information, the optical storage medium exhibiting an opticaltransmittance which varies when data is written by means of the lightbeam, wherein: in a first data storage layer, the address area has afirst address area and a second address area which are adjacent to eachother along tracks, the first data storage layer being one of the datastorage layers which is located closest to a light-striking surface ofthe medium, a second data storage layer being another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface; the address information portions ineither one of the first and second address areas are formed in thoseaddress tracks which extend from the land, and the address informationportions in the other one of the first and second address areas areformed in those address tracks which extend from the groove; and eitheran area where the address information portions are formed or an areawhere no address information portions are formed is continuouslyrecorded.
 37. The optical storage medium as set forth in claim 36,wherein the data storage layers exhibit a lower optical reflectance inrecorded areas than in non-recorded areas.
 38. An optical read/writeapparatus causing a read/write light beam from illuminating means tostrike only one side of an optical storage medium including stacked datastorage layers each of which is readable/writeable separately from theother layers by means of only a light beam striking one side of theoptical storage medium, each of the data storage layers having at leastone address area where there are collectively formed address informationportions representing address information, the optical storage mediumexhibiting an optical transmittance which varies when data is written bymeans of the light beam, the optical read/write apparatus comprisingcontrolling means for controlling the illuminating means so that theaddress area of a first data storage layer includes a recorded areaexhibiting a varied transmittance and a non-recorded area exhibiting anoriginal transmittance, the first data storage layer being one of thedata storage layers which is located closest to a light-striking surfaceof the medium, a second data storage layer being another of the datastorage layers which is located next to the first data storage layer,opposite the -light-striking surface.
 39. The optical read/writeapparatus as set forth in claim 38, wherein the storage medium exhibitsa lower optical reflectance in the recorded areas of the data storagelayer than in the non-recorded areas thereof.
 40. An optical read/writeapparatus causing a read/write light beam from illuminating means tostrike only one side of an optical storage medium including stacked datastorage layers each of which is readable/writeable separately from theother layers by means of only a light beam striking one side of theoptical storage medium, each of the data storage layers having addresstracks and at least one address area where there are collectively formedaddress information portions representing address information, opticalstorage medium exhibiting an optical transmittance which varies whendata is written by means of the light beam, the optical read/writeapparatus comprising controlling means for controlling the illuminatingmeans so that one of every adjacent two of the address tracks in theaddress area of a first data storage layer is continuously recorded bymeans of the incident light, and the other one is unrecorded, the firstdata storage layer being one of the data storage layers which is locatedclosest to a light-striking surface of the medium, a second data storagelayer being another of the data storage layers which is located next tothe first data storage layer, opposite the light-striking surface. 41.The optical read/write apparatus as set forth in claim 40, wherein thecontrolling means, after reproducing the address information, controlsthe illuminating means based on the obtained address information so thatone of every adjacent two of the address tracks is continuously recordedand the other one is unrecorded.
 42. The optical read/write apparatus asset forth in claim 40, wherein the storage medium exhibits a loweroptical reflectance in recorded areas of the data storage layer than innon-recorded areas thereof.
 43. An optical read/write apparatus causinga read/write light beam from illuminating means to strike only one sideof an optical storage medium including stacked data storage layers eachof which is readable/writeable separately from the other layers by meansof only a light beam striking one side of the optical storage medium,each of the data storage layers having address tracks and at least oneaddress area where there are collectively formed address informationportions representing address information, optical storage mediumexhibiting an optical transmittance which varies when data is written bymeans of the light beam, wherein: the optical storage medium is suchthat each of the address tracks in the address area of a first datastorage layer has a judgement mark to show whether the address track isto be continuously recorded or left unrecorded, the first data storagelayer being one of the data storage layers which is located closest to alight-striking surface of the medium, a second data storage layer beinganother of the data storage layers which is located next to the firstdata storage layer, opposite the light-striking surface; and the opticalread/write apparatus comprises controlling means for determining basedon information reproduced from the judgement mark whether each of theaddress tracks in the address area is to be continuously recorded orleft unrecorded and controlling the illuminating means according to aresult of the determination so that each of the address tracks is to beeither continuously recorded or left unrecorded.
 44. The opticalread/write apparatus as set forth in claim 43, wherein the storagemedium exhibits a lower optical reflectance in recorded areas of thedata storage layer than in non-recorded areas thereof.
 45. An opticalread/write apparatus causing a read/write light beam from illuminatingmeans to strike only one side of an optical storage medium includingstacked data storage layers each of which is readable/writeable on botha land and a groove formed on the data storage layer separately from theother layers by means of only a light beam striking one side of theoptical storage medium, each of the data storage layers having addresstracks and at least one address area where there are collectively formedaddress information portions representing address information, theoptical storage medium exhibiting an optical transmittance which varieswhen data is written by means of the light beam, the optical read/writeapparatus comprising controlling means for controlling the illuminatingmeans so that in the address area of a first data storage layer, eitherthose address tracks which extend from the land or those which extendfrom the groove are continuously recorded by means of the incidentlight, and the others are unrecorded, the first data storage layer beingone of the data storage layers which is located closest to alight-striking surface of the medium, a second data storage layer beinganother of the data storage layers which is located next to the firstdata storage layer, opposite the light-striking surface.
 46. The opticalread/write apparatus as set forth in claim 45, wherein the storagemedium exhibits a lower optical reflectance in recorded areas of thedata storage layer than in non-recorded areas thereof.
 47. An opticalread/write apparatus causing a read/write light beam from illuminatingmeans to strike only one side of an optical storage medium includingstacked data storage layers each of which is readable/writeable on botha land and a groove formed on the data storage layer separately from theother layers by means of only a light beam striking one side of theoptical storage medium, each of the data storage layers having addresstracks and at least one address area where there are collectively formedaddress information portions representing address information, theoptical storage medium exhibiting an optical transmittance which varieswhen data is written by means of the light beam, the optical read/writeapparatus comprising controlling means for controlling the illuminatingmeans so that: in a first data storage layer. the address area has afirst address area and a second address area which are adjacent to eachother along tracks, the first data storage layer being one of the datastorage layers which is located closest to a light-striking surface ofthe medium, a second data storage layer being another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface; and when the address informationportions in either one of the first and second address areas are formedin those address tracks which extend from the land, and the addressinformation portions in the other one of the first and second addressareas are formed in those address tracks which extend from the groove,either an area where the address information portions are formed or anarea where no address information portions are formed is continuouslyrecorded in the first and second address areas.
 48. The opticalread/write apparatus as set forth in claim 47, wherein the storagemedium has a lower optical reflectance in recorded areas of the datastorage layer than in non-recorded areas thereof.
 49. An opticalread/write method, comprising the step of causing a read/write lightbeam to strike only one side of an optical storage medium includingstacked data storage layers each of which is readable/writeableseparately from the other layers by means of only a light beam strikingone side of the optical storage medium, each of the data storage layershaving at least one address area where there are collectively formedaddress information portions representing address information, theoptical storage medium exhibiting an optical transmittance which varieswhen data is written by means of the light beam, wherein the addressarea in a first data storage layer includes a recorded area exhibiting avaried transmittance and a non-recorded area exhibiting an originaltransmittance, the first data storage layer being one of the datastorage layers which is located closest to a light-striking surface ofthe medium, a second data storage layer being another of the datastorage layers which is located next to the first data storage layer,opposite the light-striking surface.
 50. The optical read/write methodas set forth in claim 49, wherein the storage medium exhibits a loweroptical reflectance in recorded areas of the data storage layer than innon-recorded areas thereof.
 51. An optical read/write method, comprisingthe step of causing a read/write light beam to strike only one side ofan optical storage medium including stacked data storage layers each ofwhich is readable/writeable separately from the other layers by means ofonly a light beam striking one side of the optical storage medium, eachof the data storage layers having address tracks and at least oneaddress area where there are collectively formed address informationportions representing address information, the optical storage mediumexhibiting an optical transmittance which varies when data is written bymeans of the light beam, wherein the method further comprises the stepof continuously recording one of every adjacent two of the addresstracks in the address area of a first data storage layer by means of theincident light, while leaving the other one unrecorded, the first datastorage layer being one of the data storage layers which is locatedclosest to a light-striking surface of the medium, a second data storagelayer being another of the data storage layers which is located next tothe first data storage layer, opposite the light-striking surface. 52.The optical read/write method as set forth in claim 51, wherein one ofevery adjacent two of the address tracks in the address area of a firstdata storage layer is continuously recorded by means of the incidentlight, and the other one is unrecorded, after address information isread, based on a resultant address information.
 53. An opticalread/write method, comprising the step of causing a read/write lightbeam from illuminating means to strike only one side of an opticalstorage medium including stacked data storage layers each of which isreadable/writeable separately from the other layers by means of only alight beam striking one side of the optical storage medium, each of thedata storage layers having address tracks and at least one address areawhere there are collectively formed address information portionsrepresenting address information, the optical storage medium exhibitingan optical transmittance which varies when data is written by means ofthe light beam, wherein: the optical storage medium is such that each ofthe address tracks in the address area of a first data storage layer hasa judgement mark to show whether the address track is to be continuouslyrecorded or left unrecorded, the first data storage layer being one ofthe data storage layers which is located closest to a light-strikingsurface of the medium, a second data storage layer being another of thedata storage layers which is located next to the first data storagelayer, opposite the light-striking surface; and the method furthercomprises the steps of determining based on information reproduced fromthe judgement mark whether each of the address tracks in the addressarea is to be continuously recorded or left unrecorded and causing eachof the address tracks to be either continuously recorded or leftunrecorded by means of the incident light according to a result of thedetermination.
 54. An optical read/write method, comprising the step ofcausing a read/write light beam to strike only one side of an opticalstorage medium including stacked data storage layers each of which isreadable/writeable on both a land and a groove formed on the datastorage layer separately from the other layers by means of only a lightbeam striking one side of the optical storage medium, each of the datastorage layers having address tracks and at last one address area wherethere are collectively formed address information portions representingaddress information, the optical storage medium exhibiting an opticaltransmittance which varies when data is written by means of the lightbeam, wherein in the address area of a first data storage layer, eitherthose address tracks which extend from the land or those which extendfrom the groove are continuously recorded by means of the incidentlight, and the others are unrecorded, the first data storage layer beingone of the data storage layers which is located closest to alight-striking surface of the medium, a second data storage layer beinganother of the data storage layers which is located next to the firstdata storage layer, opposite the light-striking surface.
 55. An opticalread/write method, comprising the step of causing a read/write lightbeam to strike only one side of an optical storage medium includingstacked data storage layers each of which is readable/writeable on botha land and a groove formed on the data storage layer separately from theother layers by means of only a light beam striking one side of theoptical storage medium, each of the data storage layers having addresstracks and at last one address area where there are collectively formedaddress information portions representing address information, theoptical storage medium exhibiting an optical transmittance which varieswhen data is written by means of the light beam, wherein: in a firstdata storage layer, the address area has a first address area and asecond address area which are adjacent to each other along tracks, thefirst data storage layer being one of the data storage layers which islocated closest to a light-striking surface of the medium, a second datastorage layer being another of the data storage layers which is locatednext to the first data storage layer, opposite the light-strikingsurface; and the method further comprises the step of, when the addressinformation portions in either one of the first and second address areasare formed in those address tracks which extend from the land, and theaddress information portions in the other one of the first and secondaddress areas are formed in those address tracks which extend from thegroove, continuously recording either an area where the addressinformation portions are formed or an area where no address informationportions are formed in the first and second address areas by means ofthe incident light.
 56. An optical storage medium, comprising: onelight-striking-side storage layer provided as a data storage layer on alight-striking side; and one or more opposite-side storage layersprovided as data storage layers opposite the light-striking side fromthe light-striking-side storage layer, wherein one of the opposite-sidestorage layers which is, as a last data storage layer, most distancedfrom the light-striking-side storage layer has a prepit area whichincludes preformed pits representative of data.
 57. The optical storagemedium as set forth in claim 56, wherein each of the data storage layersexcept for the last data storage layer has a pseudo-recording area atsuch a position that allows light to be transmitted to the prepit area,the pseudo-recording area, when fully prerecorded, exhibiting a higheroptical transmittance than other areas.
 58. The optical storage mediumas set forth in claim 56, wherein the data storage layers exhibit alower optical reflectance in recorded areas than in non-recorded area.59. An optical read/write apparatus causing a read/write light beam fromilluminating means to strike only one side of an optical storage mediumincluding: one light-striking-side storage layer provided as a datastorage layer on a light-striking side; and one or more opposite-sidestorage layers as data storage layers provided opposite thelight-striking side from the light-striking-side storage layer, wherein:the medium is such that one of the opposite-side storage layers whichis, as a last data storage layer, most distanced from thelight-striking-side storage layer has a prepit area which includespreformed pits representative of data: and the optical read/writeapparatus comprises: envelope detecting means for detecting an envelopeof a reproduction signal obtained from the prepit area; mean levelproducing means for producing a mean level of the detected envelope; anddigital converting means for converting the reproduction signal to adigital signal using the mean level as a reference.
 60. The opticalread/write apparatus as set forth in claim 59, wherein the opticalstorage medium exhibits a lower optical reflectance in recorded areas ofthe data storage layers than in non-recorded areas thereof.
 61. Anoptical read/write apparatus causing a read/write light beam fromilluminating means to strike only one side of an optical storage mediumincluding: one light-striking-side storage layer provided as a datastorage layer on a light-striking side; and one or more opposite-sidestorage layers as data storage layers provided opposite thelight-striking side from the light-striking-side storage layer, wherein:the medium is such that one of the opposite-side storage layers whichis, as a last data storage layer, most distanced from thelight-striking-side storage layer has a prepit area which includespreformed pits representative of data: and the optical read/writeapparatus comprises: low frequency variation removing means for removinglow frequency variations from the reproduction signal obtained from theprepit area; and digital converting means for converting thereproduction signal from which the low frequency variations are removedto a digital signal using a constant voltage as a reference.
 62. Theoptical read/write apparatus as set forth in claim 61, wherein theoptical storage medium exhibits a lower optical reflectance in recordedareas of the data storage layers than in non-recorded areas thereof. 63.An optical read/write apparatus causing a read/write light beam fromilluminating means to strike only one side of an optical storage mediumincluding: one light-striking-side storage layer provided as a datastorage layer on a light-striking side; and one or more opposite-sidestorage layers as data storage layers provided opposite thelight-striking side from the light-striking-side storage layer, wherein:the medium is such that one of the opposite-side storage layers whichis, as a last data storage layer, most distanced from thelight-striking-side storage layer has a prepit area which includespreformed pits representative of data and that each of the data storagelayers except for the last data storage layer has a pseudo-recordingarea at such a position that allows light to be transmitted to theprepit area, the pseudo-recording area, when fully prerecorded,exhibiting a higher optical transmittance than other areas; and theoptical read/write apparatus comprises: recording status checking meansfor checking whether the pseudo-recording area is fully recorded or notbased on a reproduction signal obtained from the pseudo-recording area;and pseudo-recording means for fully recording data in thepseudo-recording area if the pseudo-recording area is not fullyrecorded.
 64. The optical read/write apparatus as set forth in claim 63,wherein the optical storage medium exhibits a lower optical reflectancein recorded areas of the data storage layers than in non-recorded areas.65. An optical read/write method using an optical storage mediumincluding: one light-striking-side storage layer provided as a datastorage layer on a light-striking side; and one or more opposite-sidestorage layers as data storage layers provided opposite thelight-striking side from the light-striking-side storage layer, themethod comprising the step of causing a read/write light beam fromilluminating means to strike only one side of the optical storagemedium, wherein the medium is such that one of the opposite-side storagelayers which is, as a last data storage layer, most distanced from thelight-striking-side storage layer has a prepit area which includespreformed pits representative of data; and the method further comprisesthe steps of: producing a mean level of an envelope of a reproductionsignal obtained from the prepit area; and converting the reproductionsignal to a digital signal using the mean level as a reference.
 66. Anoptical read/write method using an optical storage medium including: onelight-striking-side storage layer provided as a data storage layer on alight-striking side; and one or more opposite-side storage layers asdata storage layers provided opposite the light-striking side from thelight-striking-side storage layer, the method comprising the step ofcausing a read/write light beam from illuminating means to strike onlyone side of the optical storage medium, wherein the medium is such thatone of the opposite-side storage layers which is, as a last data storagelayer, most distanced from the light-striking-side storage layer has aprepit area which includes preformed pits representative of data; andthe method further comprises the steps of: removing low frequencyvariations from the reproduction signal obtained from the prepit area;and converting the reproduction signal from which the low frequencyvariations are removed to a digital signal using a constant voltage as areference.
 67. An optical read/write method, comprising the step ofcausing a read/write light beam from illuminating means to strike onlyone side of an optical storage medium including: one light-striking-sidestorage layer provided as a data storage layer on a light-striking side;and one or more opposite-side storage layers as data storage layersprovided opposite the light-striking side from the light-striking-sidestorage layer, wherein the medium is such that one of the opposite-sidestorage layers which is, as a last data storage layer, most distancedfrom the light-striking-side storage layer has a prepit area whichincludes preformed pits representative of data and that each of the datastorage layers except for the last data storage layer has apseudo-recording area at such a position that allows light to betransmitted to the prepit area, the pseudo-recording area, when fullyprerecorded, exhibiting a higher optical transmittance than other areas;the method further comprises the step of fully recording thepseudo-recording area so that light can transmit the prepit area.
 68. Anoptical storage medium, comprising: one light-striking-side storagelayer provided as a data storage layer on a light-striking side; and oneor more opposite-side storage layers provided as data storage layersopposite the light-striking side from the light-striking-side storagelayer, wherein: the light-striking-side storage layer has a prepit areawhich includes preformed pits representative of data; and thelight-striking-side storage layer has a larger optically transparent,recordable area than do the opposite-side storage layers.
 69. Theoptical storage medium as set forth in claim 68, wherein the recordableareas of the data storage layers except for a last data storage layerwhich is most distanced from the light-striking-side storage layerexhibit, when fully recorded, a higher optical transmittance than otherareas.
 70. The optical storage medium as set forth in claim 68, whereinthe data storage layers exhibit a lower optical reflectance in recordedareas than in non-recorded areas.
 71. An optical storage medium,comprising: one light-striking-side storage layer provided as a datastorage layer on a light-striking side; and one or more opposite-sidestorage layers provided as data storage layers opposite thelight-striking side from the light-striking-side storage layer, wherein:the light-striking-side storage layer has a prepit area which includespreformed pits representative of data; and the prepit area allowstransmission of light so that light reaches the opposite-side storagelayers, at a transmittance substantially equal to that of a recordablearea of the light-striking-side storage layer.
 72. The optical storagemedium as set forth in claim 71, wherein recordable areas of the datastorage layers except for a last data storage layer which is mostdistanced from the light-striking-side storage layer exhibit, when fullyrecorded, a higher optical transmittance than other areas.
 73. Theoptical storage medium as set forth in claim 71, wherein the prepitarea, under such illumination to fully record the prepit areasubstantially identically to the recordable area, exhibits a highoptical transmittance substantially equal to that of the recordablearea.
 74. The optical storage medium as set forth in claim 73, whereinon a pit row of the pits in the prepit area, there is formed acontinuous, fully recorded storage area with neither the pits norintervening portions between the pits left unrecorded, so that a fullyrecorded portion occupies a substantially equal area in a part wherelight is concentrated in the recordable area and in a part where lightis concentrated in the prepit area.
 75. The optical storage medium asset forth in claim 71, wherein the data storage layer exhibits a loweroptical reflectance in recorded areas than in

non-recorded areas.
 76. An optical read/write apparatus causing aread/write light beam from illuminating means to strike only one side ofan optical storage medium including: one light-striking-side storagelayer provided as a data storage layer on a light-striking side; and oneor more opposite-side storage layers as data storage layers providedopposite the light-striking side from the light-striking-side storagelayer, wherein: the optical storage medium is such that: thelight-striking-side storage layer has a prepit area which includespreformed pits representative of date; the light-striking-side storagelayer has a larger optically transparent, recordable area than do theopposite-side storage layers; and the recordable areas of the datastorage layers except for a last data storage layer which is mostdistanced from the light-striking-side storage layer exhibit, when fullyrecorded, a higher optical transmittance than other areas; and theoptical read/write apparatus comprises controlling means for controllingthe illuminating means so that the recordable areas of the opposite-sidestorage layers located next to the light-striking-side storage layer areread/written after the recordable area of the light-striking-sidestorage layer is fully recorded.
 77. An optical read/write apparatuscausing a read/write light beam from illuminating means to strike onlyone side of an optical storage medium including: one light-striking-sidestorage layer provided as a data storage layer on a light-striking side;and one or more opposite-side storage layers as data storage layersprovided opposite the light-striking side from the light-striking-sidestorage layer, wherein: the optical storage medium is such that: thelight-striking-side storage layer has a prepit area which includespreformed pits representative of data; the prepit area allowstransmission of light so that light reaches the opposite-side storagelayers, at a transmittance substantially equal to that of a recordablearea of the light-striking-side storage layer; and recordable areas ofthe data storage layers except for a last data storage layer which ismost distanced from the light-striking-side storage layer exhibit, whenfully recorded, a higher optical transmittance than other areas; and theoptical read/write apparatus comprises controlling means for controllingthe illuminating means so that the recordable areas of the opposite-sidestorage layers located next to the light-striking-side storage layer areread/written after the recordable area of the light-striking-sidestorage layer is fully recorded.
 78. An optical read/write apparatuscausing a read/write light beam from illuminating means to strike onlyone side of an optical storage medium including: one light-striking-sidestorage layer provided as a data storage layer on a light-striking side;and one or more opposite-side storage layers as data storage layersprovided opposite the light-striking side from the light-striking-sidestorage layer, wherein: the optical storage medium is such that: thelight-striking-side storage layer has a prepit area which includespreformed pits representative of data; the prepit area allowstransmission of light so that light reaches the opposite-side storagelayers, at a transmittance substantially equal to that of a recordablearea of the light-striking-side storage layer; and the prepit area,under such illumination to fully record the prepit area substantiallyidentically to the recordable area, exhibits a high opticaltransmittance substantially equal to that of the recordable area; theoptical read/write apparatus comprises: continuous storage area checkingmeans for checking based on a signal reproduced from the prepit areawhether or not the prepit area has a continuous storage area where areasinterposed between the pits are continuously and fully recorded as to apit row of the pits; and continuous recording means for performing suchrecording that on the pit row in the prepit area where the continuousstorage area is not present, there is formed the continuous storage areaso that a fully recorded portion occupies a substantially equal area ina part where light is concentrated in the recordable area and in a partwhere light is concentrated in the prepit area.
 79. The opticalread/write apparatus as set forth in claim 78, wherein the opticalstorage medium has a lower optical reflectance in recorded areas of thedata storage layer than in non-recorded areas.
 80. An optical read/writemethod using an optical storage medium including: onelight-striking-side storage layer provided as a data storage layer on alight-striking side; and one or more opposite-side storage layers asdata storage layers provided opposite the light-striking side from thelight-striking-side storage layer, the method comprising the step ofcausing a read/write light beam from illuminating means to strike onlyone side of the optical storage medium, wherein: the optical storagemedium is such that the light-striking-side storage layer has a prepitarea which includes preformed pits representative of data; and theprepit area allows transmission of light so that light reaches theopposite-side storage layers, at a transmittance substantially equal tothat of a recordable area of the light-striking-side storage layer; andthe optical read/write method comprises the step of reading/writing therecordable areas of the opposite-side storage layers located next to thelight-striking-side storage layer after fully recording the recordablearea of the light-striking-side storage layer.
 81. An optical read/writemethod using an optical storage medium including: onelight-striking-side storage layer provided as a data storage layer on alight-striking side; and one or more opposite-side storage layers asdata storage layers provided opposite the light-striking side from thelight-striking-side storage layer, the method comprising the step ofcausing a read/write light beam from illuminating means to strike onlyone side of the optical storage medium, wherein: the optical storagemedium is such that: the light-striking-side storage layer has a prepitarea which includes preformed pits representative of data; the prepitarea allows transmission of light so that light reaches theopposite-side storage layers, at a transmittance substantially equal tothat of a recordable area of the light-striking-side storage layer; andthe prepit area, under such illumination to fully record the prepit areasubstantially identically to the recordable area, exhibits a highoptical transmittance substantially equal to that of the recordablearea; the method comprises the step of performing such recording that asto a pit row of the pits to form a continuous storage area on the pitrow in the prepit area in the continuous storage area where areasinterposed between the pits are continuously and fully recorded is notpresent so that a fully recorded portion occupies a substantially equalarea in a part where light is concentrated in the recordable area and ina part where light is concentrated in the prepit area.